Columtiia  ®nibersJitp 

^cfjool  of  Bental  anb  0val  ^urgetrp 


J^eference  %ihxaxp 


^ 


A 

TEXT-BOOK   OF 
HISTOLOGY 


BY 

FREDERICK  R.  BAILEY,  A.  M.,  M.  D. 


FOURTH  REVISED  EDITION 

PROFUSELY  ILLUSTRATED 


NEW  YORK 
WILLIAM   WOOD   AND   COMPANY 

M  D  C  C  C  C  X  1 1 1 


Copyright,  1913 
By  WILLIAM  WOOD  AND  COMPANY 


THE . MAPLE . PRESS- YORK. PA 


PREFACE  TO  THE  FOURTH  EDITION 


The  very  gratifying  approval  which  the  previous  editions  of 
the  Text-book  received  has  made  it  seem  unwise  to  attempt  any 
change  in  the  general  plan  and  scope  of  the  work  as  outlined  in  the 
preface  to  the  first  edition.  The  text  has  been  thoroughly  revised, 
some  parts  of  it  rewritten.  Some  figures  have  been  replaced  by 
new  ones  and  a  considerable  number  of  new  figures,  have  been 
added.  For  these  the  writer  wishes  to  acknowledge  his  obliga- 
tions. To  Prof.  H.  von  W.  Schulte  and  to  Mr.  A.  M.  Miller  the 
writer  is  indebted  for  many  valuable  criticisms  and  suggestions. 
The  chapter  on  the  nervous  system  which  was  rewritten  by  Dr.  Oliver 
S.  Strong  for  the  third  edition,  has  been  revised  by  him  for  the 
present  edition.  For  Dr.  Strong's  careful  and  painstaking  work 
on  this  chapter,  for  his  thoroughly  original  treatment  of  his  subject, 
and  for  the  original  drawings  and  photographs  in  this  chapter,  the 
author  wishes  again  to  express  his  most  grateful  appreciation. 
Dr.  Strong  wishes  to  acknowledge  his  indebtedness  to  Dr.  Adolf 
Meyer  for  many  ideas  and  terms  found  valuable  in  the  preparation 
of  the  chapter  on  the  nervous  system. 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/textbookofhistol1913bail 


PREFACE  TO  THE  FIRST  EDITION 


The  primary  aim  of  the  writer  in  the  preparation  of  these  pages 
has  been  to  give  to  the  student  of  medicine  a  text-book  of  histology 
for  use  in  connection  with  practical  laboratory  instruction,  and  espe- 
cially to  furnish  to  the  instructor  of  histology  a  satisfactory  manual 
for  classroom  teaching.  With  these  objects  in  view,  the  text  has 
been  made  as  concise  as  possible  consistent  with  clearness,  and  the 
writer  has  attempted  to  make  the  more  essential  elements  stand  out 
somewhat  from  the  necessarily  accompanying  details. 

It  has  been  impossible  to  accomplish  this  without  some  sacrifice 
of  uniformity  of  treatment  and  of  logical  sequence.  This  is  especially 
noticeable  in  the  chapter  on  the  nervous  system,  which  has  been  made 
much  fuller  and  more  "practical"  than  is  usual.  The  author's  reason 
for  the  method  of  treatment  there  adopted  and  for  the  considerable 
amount  of  anatomy  which  this  chapter  contains  is  the  apparent 
success  the  method  has  met  with  in  the  teaching  of  this  always 
difficult  subject  to  students. 

The  chapter  on  general  technic  is  intended  to  furnish  the  student 
with  only  the  more  essential  laboratory  methods.  For  special  and 
more  elaborate  methods  the  student  is  referred  to  the  special  works 
on  technic  mentioned  at  the  close  of  the  chapter.  The  special  tech- 
nic given  in  connection  with  the  different  tissues  and  organs  is  in 
most  cases  such  as  can  be  conveniently  used  for  the  preparation  of 
class  sections. 

The  original  illustrations  are  from  drawings  by  Mr.  A.  M.  Miller, 
to  whom  the  writer  is  greatly  indebted  for  his  careful  and  accurate 
work.  The  uselessness  of  redrawing  perfectly  satisfactory  illustra- 
tions has  led  the  writer  to  borrow  freely  from  various  sources,  each 
cut  being  duly  accredited  to  the  work  from  which  it  has  been  taken. 
For  all  of  these  the  author  wishes  to  express  his  appreciation  and  obli- 
gation. He  is  also  deeply  indebted  to  Dr.  O.  S.  Strong  for  his  careful 
review  and  criticism  of  the  chapter  on  the  nervous  system  and  for  his 
supervision  of  the  drawing  of  Figs.  263  and  264;  to  Dr.  G.  C.  Free- 
born, his  predecessor  as  Instructor  of  Histology  at  the  College  of  Phy- 
sicians and  Surgeons,  for  many  valuable  suggestions;  and  to  Dr.  T. 
Mitchell  Prudflcn  for  his  careful  and  critical  review  of  the  author's 
copy. 


CONTENTS 


PART  I.-HISTOLOGICAL  TECHNIC 


CHAPTER  I 


General  Technic.  Page. 

General  Considerations, 3 

Examination  of  Fresh  Tissues,      3 

Dissociation  of  Tissue  Elements, 4 

Teasing, 4 

INIaceration,      4 

Preparation  of  Sections, S 

Fixation, S 

Hardening, ° 

Preserving, 9 

Decalcifying, ^° 

Embedding,      ^^ 

Celloidin  Embedding, ^'^ 

Paraffin  Embedding, ^3 

Section  Cutting, ^4 

Celloidin  Sections, ^4 

Paraffin  Sections, ^5 

Frozen  Sections, ^5 

Staining, ^7 

Nuclear  Dyes,      ^7 

Plasma  Dyes, ^9 

•     Staining  Sections, ^° 

Staining  in  Bulk, ^i 

Mounting, ^^ 

Staining  and  Mounting  l*araQin  Sections, 23 

Injection, ^S 

CHAPTER  II 

Special  Staining  Methods. 

Silver  Nitrate  Method  of  Staining  the  Intercellular  Substance, 28 

Chlorid  of  Gold  for  Demonstrating  Connective-tissue  Cells, 28 

Weigert's  Elastic  Tissue  Stain, 28 

Verhoeff's  Differential  Elastic  Tissue  Slain, 28 

Golgi's  (!hromc-silver  for  staining  Secretory  'I'ubiilcs 29 

Mallory's  Phosphomolybdic  Acid  Ha;matoxylin  Stain  for  Connective  Tissue,  29 

Mallory's  Phosphotungstic  Acid  Haematoxylin  Stain  for  Connective  Tissue,  .  30 

vii 


viii  CONTENTS 

Page 

Mallory's  Aniline  Blue  Stain  for  Connective  Tissue 3° 

Maresh's  Modification  of  Bielschowsky's  Stain  for  the  Finer  Connective  Tissue 

Fibrils, ^i 

Osmic  Acid  Stain  for  Fat, 3i 

Jenner's  Blood  Stain, 3 1 

CHAPTER  III 

Special  Neurological  Staining  Methods. 

Weigert's  Method  of  Staining  Medullated  Nerve  Fibres, 32 

Weigert-Pal  Method,      - 33 

Marchi's  Method  for  Staining  Degenerating  Nerves, 34 

Golgi  Methods  of  Staining  Nerve  Tissue, 35 

Slow  Method, 35 

Rapid  Method, 35 

Mixed  Method, 35 

Formalin  Bichromate  Method, ■, 3^ 

Bichloride  Method, 36 

Golgi-Cox  Method, 36 

Cajal's  Method, 37 

Nissl's  Method, •    •    ■  38 

General  References  on  Technic, 39 


PART  II.-THE  CELL 


CHAPTER  I 


The  Cell,    . 43 

General  Structure, 43 

Structiure  of  a  Typical  Cell, .  43 

The  Cell  Body, 44 

The  Cell  Membrane, 47 

The  Nucleus, 47 

The  Centrosome, 49 

Vital  Properties  of  Cells, .  50 

Metabolism, 50 

Function, 51 

Irritability, 51 

Motion, 51 

Amoeboid, 52 

Protoplasmic, 52 

Ciliary, 52 

Reproduction, 52 

Direct  Cell-division, 53 

Indurect  Cell-division, 53 

Fertilization  of  the  Ovum,     . ■ 58 

Technic, ■ 63 

References  for  further  study, 64 


CONTENTS  IX 

PART  III.-THE  TISSUES 


CHAPTER  I 

Page 

Histogenesis — Classification, 67 

Tissues  Derived  from  Ectoderm,      67 

Tissues  Derived  from  Entoderm, 67 

Tissues  Derived  from  Mesoderm, 68 

CHAPTER  II 

Epithelium  (Including  Mesothelium  and  Endothelium), 69 

Histogenesis, 69 

General  Characteristics, 69 

Classification,          7° 

Simple  Epithelium, 7^ 

Simple  Squamous, 7^ 

Simple  Columnar, 7^ 

Pseudostratified,      73 

Stratified  Epithelium, 73 

Stratified  Squamous, 73 

Stratified  Columnar, 74 

Transitional, 74 

Modified  Forms  of  Epithelium, 75 

Ciliated  Epithelium, ■,    ■    •  75 

Pigmented  Epithelium, 76 

Glandular  EpitheUum, 77 

Neuro-epithelium, 77 

Mesothelium  and  Endothelium, 77 

Technic, 7^ 

CHAPTER  III 

The  Connectrtl  Tissues, So 

General  Characteristics, 80 

Classification,       81 

Development, 81 

Connective  Tissue,  Proper 82 

Embryonal  Connective  Tissue, 82 

Fibrillar  Connective  Tissue, 82 

Connective-tissue  Cells, 83 

Intercellular  Substance, 86 

Areolar  or  Loose  Connective  Tissue, 87 

Fat  Tissue, 87 

Formed  Connective  Ti.ssue, 91 

Tendons  and  Ligaments, 91 

Elastic  Tissue, 92 

Reticular  Tissue, 94 

Technic, 95 

Cartilage,      97 

Hyaline, 98 


x:  CONTENTS 

Page 

Elastic, 99 

Fibrous, 99 

Technic, 100 

Bone  Tissue, 100 

Technic, 102 

CHAPTER  IV 

The  Blood, 103 

Red  Blood  Cells, 103 

White  Blood  Cells, 105 

Blood  Platelets, 108 

Blood  Dust, . 108 

Development, 108 

Technic, no 

CHAPTER  V 

Muscle  Tissxje,     in 

Involuntary  Smooth  Muscle, in 

Voluntary  Striated  Muscle, in 

Involuntary  Striated  Muscle  (Heart  Muscle), 119 

Development  of  Muscle  Tissue, 122 

Technic, 124 

CHAPTER  VI 

Nerve  Tissue, 126 

The  Neurone, 126 

General  Structure, 126 

The  Cell  Body, 126 

The  Nucleus, 127 

The  Cytoplasm, 128 

Neurofibrils, 128 

Perifibrillar  Substance, 128 

Chromophilic  Bodies, 129 

The  Protoplasmic  Processes  ot  Dendrites,      131 

The  Axone, 132 

Non-meduUated  Axones  (Non-medullated  Nerve  Fibres), .  132 

Medullated  Axones  (Medullated  Nerve  Fibres), 133 

Theories  as  to  Physiology  of  the  Neurone, 137 

Significance  of  Degenerative  Changes  in  the  Neurone, 139 

Neuroglia, 142 

Technic, 144 

General  References, 145 

PART  IV.— THE  ORGANS 


CHAPTER  I 


The  Circulatory  System, 151 

:  ,     The  Blood-vessel  System, -    •    •    iSi 


CONTENTS  ^^ 

Page 

151 

General  Structure, ^^^ 

Capillaries, j^^ 

Arteries, ....  158 

Veins, 160 

Technic, .    .  161 

The  Heart, ^^^ 

Technic, ^5, 

Development  of  the  Circulatory  System '    .    .  164 

The  Lymph-vessel  System,    •    •■ '  ^5^ 

Lymph  Capillaries,      .    .  165 

Lymph  Spaces, j5g 

Development  of  Lymph-vessel  System, '    .  166 

Technic, •    ■    ■  ^^^ 

General  References  on  Circulatory  System, 

CHAPTER  II 

167 

LYMPH.A.TIC  Organs, ^^^ 

The  Lymph  Nodes, .    .    171 

Development, 

Technic, ^-^ 

Hsmolj^mph  Nodes, .    .    17S 

Technic, ^^^ 

The  Thymus, ^^^ 

Development, j.  g 

Technic, j«g 

The  Tonsils, .    .    178 

The  Palatine  Tonsils, ^g^ 

The  Lingual  Tonsils,       ^g^ 

The  Pharj-ngcal  Tonsils, .    180 

Development, ^g^ 

Technic, .181 

The  Spleen, 187 

Technic, jg^ 

General  References, 

CHAPTER  HI 

....   188 
The  Skeletal  System ^gg 

The  Bones, ^^2 

Bone  Marrow,      ^ 

Red  Marrow, 

Yellow  Marrow, . 

Technic, ^^^ 

Development  of  Bone, 

Intramcmbranous  Development 

Intracartilaginous  Development,      ^^^ 

Subperiosteal, 

Growth  of  Bone,      203 

Technic, 204 

The  Cartilages, 


xil  CONTENTS 

Page 

Articulations, 204 

Technic, 205 

General  References, 206 

CHAPTER  IV 

The  Muscular  System. 

A  Voluntary  Muscle, 207 

Tendon  Sheaths  and  Bursse, 208 

Growth  of  Muscle, ' 209 

Technic, 211 

CHAPTER  V 

Glands  and  the  General  Structure  of  Mucous  Membranes, 212 

Glands — General  Structure  and  Classification, 212 

Duct  Glands, 215 

Tubular  Glands 215 

Aveolar  Glands, 217 

Ductless  Glands, 217 

General  Structure  of  Mucous  Membranes, 218 

CHAPTER  VI 

The  Digestive  System, 220 

Anatomical  Divisions, 220 

The  Headgut, 221 

The  Mouth,      221 

The  Mucous  Membrane  of  the  Mouth, 221 

Glands  of  the  Oral  Mucosa, 221 

Technic, 223 

The  Tongue, 223 

Technic, ^ 227 

The  Teeth, * 227 

Development  of  the  Teeth, 238 

Technic, 242 

The  Pharynx, 242 

Technic, 243 

The  Foregut, ' 243 

The  Oesophagus,      243 

Technic, 245 

General  Structure  of  the  WaUs  of  the  Gastro-intestinal  Canal,      ....  245 

The  Stomach, 247 

Technic, 254 

The  Midgut, ■ 255 

The  Small  Intestine, 255 

Peyer's  Patches, 260 

The  Endgut, 263 

The  Large  Intestine, 263 

The  Vermiform  Appendix, 265 

The  Rectum, 266 


CONTENTS  X"l 

Page 

The  Peritoneum,  Mesentery,  and  Omentum, 267 

Blood-vessels  of  the  Stomach  and  Intestine, 268 

Lymphatics  of  the  Stomach  and  Intestine, 270 

Nerves  of  the  Stomach  and  Intestine, 270 

Secretion  and  the  Absorption, ^7i 

Technic, '^ 

The  Larger  Glands  of  the  Digestive  System, 275 

The  SaUvary  Glands,      ^^0 

The  Parotid, ^' -^ 

The  Subungual, ^77 

The  Submaxillary, ^^8 

Technic, 

The  Pancreas,      

Technic, 

The  Liver, ^^j 

Excretory  Ducts  of  the  Liver, -^9 

The  Gall-bladder, ^^5 

Technic, ^^^ 

Development  of  the  Digestive  System, 29 

General  References, 

CHAPTER  VII 

The  Respiratory  System, "99 

TheNares, "^^ 

The  Lar>'nx, ^ 

The  Trachea, ^°^ 

Technic, ^  ^ 

The  Bronchi, 304 

The  Lungs, ^ 

Development  of  the  Respiratory  System, 3^5 

Technic, ^   ' 

General  References, ■3^' 

CHAPTER  VIII 

The  Urinary  System, 3i8 

The  Kidney, 3i8 

The  Kidney— Pelvis  and  Ureter, 329 

The  Urinary  Bladder, 33© 

Technic, ^■^^ 

General  References, 332 

CHAPTER  IX 

The  Reproductive  System, 333 

Male  Organs, 333 

The  Testis, ^^^ 

The  Seminal  Ducts, 339 

The  Ei)ididymis,      339 

The  Vas  Deferens, 34° 


xiv  CONTENTS 

Pack 

The  Seminal  Vesicles  and  Ejaculatory  Ducts, 341 

Rudimentary  Structures  Connected  with  the  Development  of  the  Genital 

System, 342 

The  Spermatozoon, 343 

Development  of  the  Spermatozoon, 344 

Technic, 346. 

The  Prostate  Gland, 347 

Cowper's  Glands, 348 

Technic, 349 

The  Penis, ,   349 

The  Urethra, ■ 351 

Technic, 352 

Female  Organs, 352 

The  Ovary, 352 

The  Graafian  Follicle, 354 

The  Corpus  Luteum, 359 

Rudimentary  organs  connected  with  the  Ovary, 363 

The  Oviduct, 364 

Technic, 365 

The  Uterus, 366 

The  Mucosa  of  the  Resting  Uterus, 367 

The  Mucosa  of  the  Menstruating  Uterus,  .    .    '. 368 

The  Mucosa  of  the  Pregnant  Uterus,      370 

The  Placenta, 371 

The  Vagina, 375 

Development  of  the  Urinary  and  Reproductive  Systems, 376 

Technic, 379 

General  References, 379 

CHAPTER  X 

The  Skin  and  its  Appendages,      380 

The  Skin,      380 

Technic, 384 

The  Nails, 385 

Technic, 387 

The  Hair,      ■ 387 

Technic, 393 

Blood-vessels  of  Skin, 393 

Technic, 395 

Development  of  Skin,  Nails,  and  Hair, 39S 

The  Mammary  Gland, 395 

Technic, 401 

General  References, 401 

CHAPTER  XI 

The  Thyreoid  and  Parathyreoid,  the  Pituitary  Body,  the  Paraganglia  and 
THE  Adrenal. 

The  Thyreoid,      402 

Development, 403 


CONTENTS  XV 

Page 

The  Parathvreoids, 404 

Technic 4o6 

The  Pituitary  Bocb', 4°; 

Paraganglia, 409 

Carotid  Glands, 4io 

Coccygeal  Gland, 4" 

Adrenal  Gland, 4i2 

General  References, 4iS 

CHAPTER  XII 

The  Nervous  System, 4^6 

Histological  Development  and  General  Structure, 4i6 

Membranes  of  the  Brain  and  Cord, 422 

Technic, 424 

The  Peripheral  Nerves, 424 

Technic, 426 

The  Afferent  Peripheral  Neurones, 426 

The  Cerebro-spinal  GangUa, 426 

The  Peripheral  Processes  of  the  Cerebro-spinal  GangUon  Cells,       .   429 
The  Central  Processes  of  the  Cerebro-spinal  Ganglion  Cells,      ...    436 

The  Sympathetic  GangUa, 436 

Technic. 44i 

The  Efferent  Peripheral  Cerebro-spinal  Neurones, 44i 

The  Spinal  Cord, 442 

Origin  of  the  Fibres  which  make  up  the  White  Matter  of  the  Cord,   ...   443 
(i)  The  Spinal  Ganglion  Cell  and  the  Origin  of  the  Posterior  Col- 
umns,      443 

(2)  Cells  Situated  in  Other  Parts  of  the  Central  Nervous  System 
which  Contribute  Axones  to  the  White  Columns  of  the  Cord,   .        444 

(3)  Root  Cells— Motor  Cells  of  the  Anterior  Horn, 444 

(4)  Column  Cells, 444 

(5)  Cells  of  Golgi  Type  II, 445 

Technic, 445 

Practical  Study, 447 

General  Topography  of  the  Cord,  Cell  Groupings,  Arrangement  of  Fibres 

and  Finer  Structure, 44° 

Practical  Study  of  Sections  through  Lumbar  Enlargement,     ....  448 

General  Topography,      44° 

Cell  Groupings,    .    .    .    . 45° 

Arrangement  of  Fibres, 452 

Finer  Structure, 453 

Blood-vessels, 454 

Variations  in  Structure  at  Different  Levels,  455 

I'ractical  Study, 455 

Section  through  the  Twelfth  Thoracic  Segment, 455 

Section  through  the  Mid-thoracic  Region,  455 

Section  through  the  Cervical  Enlargement,  455 

Fibre  Tracts  of  the  Cord, 459 

Ascending  Tracts, 46 1 

I.  Long  Ascending  Arms  of  Dorsal  Root  Fibres, 461 


xvi  CONTENTS 

Page 

II.  Spino-thalamic  Tract, -    ...    462 

III.  Dorsal  Spino-cerebellar  Tract,      463 

IV.  Ventral  Spino-cerebellar  Tract, 463 

Descending  Tracts, * 464 

I.  The  Pyramidal  Tracts, 464 

II.  The  Colliculo-spinal  Tract, 465 

III.  The  Tract  from  the  Nucleus  of  the  Posterior  or  Medial 
Longitudinal  Fasciculus, 465 

IV.  The  Rubro-spinal  Tract, 466 

V.  The  Deitero-spinal  Tract,      466 

VI.  The  Fasciculus  of  Thomas, 467 

VII.  Helweg's  Tract, 467 

VIII.  The  Septo-marginal  Tract, 467 

IX.  The  Comma  Tract  of  Schultze, 467 

Fundamental  Columns  or  Ground  Bundles, 468 

A  Two-neurone  Spinal  Reflex  Arc, .•   .    .    .  469 

A  Three-neurone  Spinal  Reflex  Arc, 469 

A  Cerebellar  Arc, 470 

A  Cerebral  or  Pallial  Arc,      471 

Technic, 47i 

The  Brain, 473 

General  Structure, 473 

Segmental  Brain  and  Nerves, 474 

Suprasegmental  Structures, '. 478 

The  Hindbrain  or  Rhombencephalon, 479 

The  Medulla  Oblongata  or  Bulb, '. 479 

The  Pons, 482' 

The  Cerebellum  (also  p.  507),       482 

Technic,    . 482 

Practical  Study, 483 

1.  Transverse  Section  of  the  Medulla  through  the  Decussation 

of  the  Pyramidal  Tracts  (Motor  Decussation), 483 

2.  Transverse  Section  of  the  Medulla  through  the  Decussation 

of  the  Fillet  or  Lemniscus  (Sensory  Decussation),   ....   485 

3.  Transverse  Section  of  the  Medulla  through  the  Lower  Part 

of  the  Inferior  Olivary  Nucleus, 487 

4.  Transverse   Section   of   the  Medulla   through   the  Middle 

of  the  Olivary  Nucleus, 401 

5.  Transverse  Section  of  the  Medulla  through  the  Entrance  of 
the  Cochlear  Root  of  Nerve  VIII, 491 

6.  Section  through  the  Hindbrain  at  Level  of  Junction  of  Pons, 
and  Cerebellum  and  Entrance  of  Vestibular  Nerve,      .    .    .   499 

7.  Transverse  Section  of  the  Hindbrain  through  the  Roots  of 
Nerves  VI  (Abducens)  and  VII  (Facial), 502 

•8.  Transverse  Section  of  the  Hindbrain  through  the  Roots  of 

Nerve  V  (Trigeminus), 504 

The  Cerebellum,      So7 

The  Cerebellar  Cortex, S09 

The  Isthmus, 5iS 

Practical  Study, 5^5 


CONTENTS  xvii 

Page 
9.  Transverse  Section  through  the  Isthmus  at  the  Exit  of  Nerve 

IV  (Trochlearis) , 515 

The  Midbrain  or  Mesencephalon, 517 

Practical  Study, Si7 

10.  Transverse  Section  through  Midbrain  at  Level  of  Anterior 
Corpora  Quadrigemina  and  Exit  of  Nerve  III  (Oculomotor),     517 

The  Forebrain  or  Prosencephalon, 522 

The  Interbrain  (Diencephalon  or  Thalamencephalon), 522 

Practical  Stud}', 524 

11.  Transverse  Section  through  the  Junction  of  Midbrain 
and  Thalamus, 524 

12.  Section  through  the  Interbrain  at  the  Level  of  the  Optic 
Chiasma, 526 

The  Endbrain  or  Telencephalon,      532 

The  Rhinencephalon,      532 

The  Corpus  Striatum, 532 

The  Pallium 532 

Practical  Study, 53S 

13.  Transverse  Section  through  the  Cerebral  Hemispheres, 
Corpora  Striata  and  Thalamus, 535 

The  Cerebral  Cortex,      536 

Technic, 543 

The  Pineal  Body, 544 

Technic, 547 

Table  of  Cranial  and  Spinal  Nerves, 545 

General  Reference  for  Further  Study, 547 


^"^^ilk. 


CHAPTER  XIII 


The  Organs  of  Special  Sense, 548 

The  Organ  of  Vision, 548 

The  Eyeball, 548 

The  Cornea, 548 

The  Chorioid, 550 

The  Ciliary  Body, 552 

The  Iris, 554 

The  Retina,      555 

The  Optic  Nerve, 559 

The  Relations  of  Optic  Nerve  to  Retina  and  Brain, 560 

The  Lens,      564 

The  Lacrymal  Apparatus,      5^7 

The  Eyelid, 567 

Development  of  the  Eye, 569 

Technic, 57° 

The  Organ  of  Hearing, 572 

The  External  Ear, 572 

The  Middle  Ear, 573 

The  Internal  Ear, 574 

The  Vestibule  and  Semicircular  Canals, 575 

The  Saccule  and  Utricle, 575 


xvm 

CONTENTS 

The  Semicircular  Canals,   .    .  Page 

The  Cochlea,    ...  575 

Development  of  the  Ear,  .    ' 576 

Technic, '       -g 

The  Organ  of  Smell,    ...'.'.' .584 

Technic, eg 

The  Organ  of  Taste,   .    .    .    .'    ' ■    •   586 

Technic, ^g„ 

General  References,         rg? 

'^""^' ■■'■'.'.'.'.'.. •    •   588 

589 


PART  I 
HISTOLOGICAL  TECHNIC 


CHAPTER  I 
GENERAL  TECHNIC 

Certain  body  fluids,  e.g.,  blood,  urine,  etc.,  may  be  examined  by 
simply  placing  them  on  a  slide  under  a  cover-glass.  A  few  tissues, 
e.g.,  thin  membranes,  such  as  the  omentum  and  the  mesentery,  may 
be  examined  fresh  in  some  such  inert  medium  as  blood  serum  or 
normal  salt  solution  (0.75-per-cent.  aqueous  solution  sodium  chlorid). 
For  such  examination  the  tissue  is  immersed  in  the  salt  solution  on  a 
slide  and  covered  with  a  cover-glass.  Most  tissues  and  organs,  how- 
ever, require  much  more  elaborate  preparation  to  render  them  suitable 
for  microscopic  examination.  Tissues  too  dense  and  thick  to  be 
readily  seen  through  with  the  microscope  must  be  so  treated  as  to 
make  them  transparent.  This  is  accomplished  either  by  pulling  the 
tissue  apart  into  fine  shreds,  teasing,  or  by  cutting  it  into  thin  slices, 
section  cutting.  Some  tissues  admit  of  teasing  in  a  fresh  condition; 
others  can  be  satisfactorily  teased  only  after  they  have  been  subjected 
to  the  action  of  a  chemical  which  breaks  down  the  substance  holding 
the  tissue  elements  together,  maceration.  Fresh  tissue  can  rarely  be 
cut  into  sections  sufficiently  thin  for  microscopic  examination.  It 
must  first  be  treated  in  such  a  manner  as  to  preserve  as  nearly  as 
possible  the  living  tissue  relations,  fixation.  If  too  soft  for  section 
cutting  it  must  next  be  put  through  a  process  known  as  hardening. 
If,  however,  as  in  the  case  of  bone,  the  tissue  is  too  hard,  it  must  be 
softened  by  dissolving  out  the  mineral  salts,  decalcification.  If  very 
thin  sections  are  to  be  cut,  it  is  further  necessary  to  impregnate  the 
tissue  with  some  fluid  substance  which  will  harden  in  the  tissue 
and  give  to  the  mass  a  firm,  even  consistency.  This  is  known  as 
embedding. 

Furthermore,  most  tissue  elements  have  refractive  indices  which 
are  so  similar  that  their  differentiation  under  the  microscope  is  often 
extremely  difficult.  To  overcome  this  difficulty,  recourse  is  had  to 
staining  the  tissue  with  dyes  which  have  an  affinity  for  certain  only 
of  the  tissue  elements,  or  which  stain  different  elements  with  different 
degrees  of  intensity.     This  is  known  as  differential  or  selective  staining. 

3 


4  HISTOLOGICAL  TECHNIC 

The  final  step  in  the  process  is  the  mounting  of  the  specimen,  after 
which  it  is  ready  for  microscopic  study. 

Only  the  more  common  procedures  used  in  the  preparation  of 
tissues  for  microscopic  study  are  described  in  this  section.  At  the 
end  of  each  section  are  given  the  technical  methods  most  satisfactory 
for  the  demonstration  of  the  tissues  described  in  that  section.  For 
other  methods  the  student  is  referred  to  special  works  upon  micro- 
scopic technic. 

Dissociation  of  Tissue  Elements 

This  method  of  preparing  tissues  for  microscopic  study  has  only 
a  limited  application,  most  specimens  being  preferably  fixed,  and  cut 
into  thin  sections.  Certain  of  the  structural  features  of  such  tissues 
as  nerves,  muscle,  and  epithelium,  which  have  but  little  intercellular 
substance  may  be  well  demonstrated  by  dissociation. 

This  is  accomplished  by  (i)  teasing,  or  (2)  maceration,  or  both. 

(i)  Teasing. — This  consists  in  pulHng  apart  fresh  or  preserved 
tissues  by  means  of  teasing  needles.  Instructive  specimens  of  such 
tissues  as  muscle  and  nerve  may  be  obtained  in  this  way. 

(2)  Maceration. — This  is  the  subjecting  of  a  tissue  to  the  action 
of  some  chemical  which  breaks  down  the  substance  uniting  the  tissue 
elements,  thus  allowing  them  either  to  fall  apart  or  to  be  more  easily 
dissociated  by  teasing.  The  most  commonly  used  macerating  fluids 
are: 

(a)  Ranvier's  Alcohol  (33-per-cent.,  made  by  adding  35  c.c.  of 
96-per-cent.  alcohol  to  65  c.c.  of  water). — Bits  of  fresh  tissue  are 
placed  in  this  fluid  for  from  twenty-four  to  forty-eight  hours.  The 
cells  may  then  be  easily  separated  by  shaking  or  by  teasing.  Ran- 
vier's alcohol  is  an  especially  satisfactory  macerating  fluid  for 
epithelia. 

(b)  Formaldehyde,  in  very  dilute  solutions  (0.2-  to  0.4-per-cent. 
commercial  formalin^) .- — ^Tissues  should  remain  in  the  formaldehyde 
solution  from  twenty-four  to  forty-eight  hours.  This  is  also  espe- 
^cially  useful  for  dissociating  epithelial  cells. 

f  j-^j  (c)  Sodium  or  Potassium  Hydrate  (30-  to  3  5-per-cent.  aqueous  solu- 
tion).— From  twenty  minutes  to  an  hour  is  usually  sufficient  to  cause 
the  tissue  elements  to  fall  apart  or  to  be  readily  pulled  apart  with  teas- 
ing needles.  If  it  is  at  any  time  desirable  to  stop  the  action  of  the 
.,    ^Commercial  formalin  is  a  40-per-cent.  solution  of  formaldehyde  gas  in  water. 


GENERAL  TECHNIC  5 

caustic  alkali,  this  may  be  accomplished  by  neutralizing  with  glacial 
acetic  acid  or  by  replacing  the  alkali  with  a  6o-per-cent.  aqueous 
solution  of  potassium  acetate.  The  specimens  may  then  be  preserved 
in  the  potassium-acetate  solution,  in  glycerin,  or  in  50-per-cent. 
alcohol.  This  dissociating  fluid  is  largely  used  for  muscle  cells  and 
fibres. 

{d)  Nitric  acid  (10-  to  20-per-cent.  aqueous  solution). — This  is 
especially  useful  for  dissociating  involuntary  and  voluntary  muscle. 

After  any  of  the  above  procedures,  the  macerating  fluid  containing 
the  tissue  elements  should  be  placed  in  a  long  tube,  allowed  to  stand 
for  a  time  and  the  fluid  decanted.  Water  is  then  poured  into  the 
tube,  the  tissues  allowed  to  settle  and  the  water  poured  off,  this  being 
repeated  until  all  trace  of  macerating  fluid  is  removed.  The  tissue 
elements  may  then  be  preserved  or  mounted  in  glycerin  or  in  glycerin 
jelly.  It  is  frequently  advisable  to  stain  the  tissues.  For  this 
purpose  alum-carmin  (p.  19)  is  especially  satisfactory.  (For  details 
see  technic  i,  p.  124  and  technic  2,  p.  124),  After  staining  and  wash- 
ing, the  tissues  may  be  preserved  or  mounted  in  glycerin,  eosin  glyc- 
erin, or  glycerin  jelly.  It  frequently  happens  that  on  examining 
dissociated  tissue  elements  after  mounting,  the  bits  of  tissue  are 
still  too  large.  This  may  be  remedied  by  gently  tapping  on  the 
cover-glass  with  a  lead  pencil. 

PREPARATION  OF  SECTIONS 
I.  Fixation 

Even  tissues,  the  structure  of  which  admits  of  their  being  exam- 
ined in  the  fresh  condition,  as  described  on  p.  3,  soon  undergo 
post-mortem  changes  if  placed  in  an  inert  medium  such  as  normal 
salt  solution  or  blood  serum.  As  a  result  they  soon  lose  their  char- 
acteristic appearance  and  disintegrate.  A  proper  killing  or  fixation 
is  therefore  the  first  step  in  the  preparation  of  most  tissues  for  micro- 
scopic study,  the  object  being  to  so  preserve  the  tissues  that  they 
retain  as  nearly  as  possiljlc,  and  more  or  less  permanently,  the  same 
structure  and  relation  which  they  had  during  life.  Fixed  tissue  may 
be  placed  in  water,  salt  soluticm,  alcohol,  etc.,  in  fact  may  be  subjected 
to  many  and  varied  manipulations  which  would  destroy  fresh  tissues, 
without  disturbing  the  relation  of  the  tissue  elements.  Fixation  of 
such  a  thin  film  of  tissue  as  a  blood  smear  may  be  accomplished  by 


6  HISTOLOGICAL  TECHNIC 

heating.  A  blood  smear  or  even  small  pieces  of  tissue  may  be  fixed 
by  exposure  to  certain  chemical  vapors  as,  e.g.,  the  vapor  of  formalin 
or  of  osmic  acid.  Fixation  is,  however,  usually  accomplished  by 
means  of  chemicals  in  solution,  the  solution  being  known  as  a  fixing 
agent  or  fixative.  The  tissue  is  immersed  in  the  fixative  and  allowed 
to  remain  there  until  fixation  is  complete.  The  pieces  of  tissue  should 
be  small,  and  large  quantities  of  the  fixative  should  be  used.  It  may 
be  necessary  to  change  the  fluid  a  number  of  times,  in  order  to  keep  it 
up  to  the  proper  strength.  The  length  of  time  required  depends 
upon  the  character  of  the  tissue  and  upon  the  fixative  used.  In 
general  it  should  be  only  long  enough  to  bring  about  the  desired  result, 
as  prolonged  immersion  in  the  fixative  may  make  the  tissue  brittle  or 
may  interfere  with  the  subsequent  treatment  of  the  tissue,  especially 
staining. 

Organs  and  even  bodies  may  be  fixed  in  toto  by  injecting  the  fixa- 
tive through  an  artery  and  allowing  it  to  escape  through  the  veins. 
After  the  injection,  the  whole  specimen  should  be  placed  in  a  large 
quantity  of  the  same  fixative.  This  method  fills  the  entire  vascular 
system  including  the  capillaries  with  the  fixative,  thus  bringing  the 
latter  into  very  prompt  and  close  contact  with  the  tissue  elements. 
The  result  is  a  very  rapid  and  accurate  fixation,  which  is  especially 
valuable  where  it  is  necessary  to  preserve  the  topographic  relations  of 
various  parts  of  an  organ  or  a  body. 

A  mercuric  chlorid  solution  (p.  8)  followed  immediately  by  strong 
alcohol  makes  a  very  good  injection  fixative.  Satisfactory  fixation 
is  largely  dependent  upon  the  freshness  of  the  tissue  when  placed  in 
the  fixative.     The  following  are  the  fixatives  in  most  common  use: 

(i)  Strong  Alcohol  (96-per-cent.). — This  is  a  rapid  fixative  and 
should  be  used  on  small  pieces  of  tissue.  The  time  required  is  from  six 
to  twenty-four  hours,  though  tissues  may  remain  longer  without 
injury.  The  alcohol  should  be  changed  after  two  or  three  hours. 
This  fixative  should  not  be  used  where  fine  histological  detail  is 
desired,  since  it  causes  some  shrinkage.  One  advantage  in  its  use  is 
the  fact  that  tissues  are  hardened  and  ready  for  embedding  at  the  end 
of  fixation. 

(2)  Dilute  Alcohol  (30-per-cent.  to  80-per-cent.) . — This,  as  a  rule, 
gives  unsatisfactory  results,  causing  much  shrinkage  of  the  tissue 
elements. 

(3)  Formalin  (2-per-cent.  to  lo-per-cent.  aqueous  solution). — 
Formalin  is  rapid  in  its  action  and  probably  has  better  penetrating 


GENERAL  TECHNIC  7 

qualities  than  any  other  fixative.  For  general  purposes  a  lo-per-cent, 
solution  (i  part  commercial  formalin  to  9  parts  water)  should  be 
used.  This  fixes  in  from  six  to  twenty-four  hours.  The  results  after 
formalin  are  not  always  good,  owing  to  the  fact  that  it  has  Uttle 
hardening  power,  and  the  subsequent  action  of  alcohol  is  Hkely  to 
cause  some  distortion  of  the  tissues.  It  acts  better  when  combined 
with  other  fixatives  than  when  used  alone.     (See  Orth's  fluid.) 

(4)  Midler's  Fluid. 

Potassium  bichromate,  2 .  5  gm. 

Sodium  sulphate,  i .  o  gm. 

Water,  100. o  c.c. 

This  fluid  gives  very  good  results,  but  is  extremely  slow  in  its  action, 
requiring  from  a  week  to  several  months.  Fairly  large  pieces  of 
tissue  may  be  fixed,  but  in  all  cases  large  quantities  of  the  fixative 
should  be  used  and  frequently  renewed. 

(5)  Orth's  Fluid. 

Miiller's  fluid  (double  strength),  [  _,       , 

Formalin,  8-per-cent.,  J 

This  is  one  of  the  best  general  fixatives.  Its  action  is  similar  to  that 
of  Miiller's  fluid  but  much  more  rapid,  fixation  being  accomplished 
in  from  twenty-four  to  forty-eight  hours,  though  specimens  may 
remain  in  the  fluid  several  days  without  disadvantage.  Fairly 
large  pieces  of  tissue  may  be  fixed  with  good  results.  The  fixative 
should  be  changed  after  a  few  hours.  Fixation  with  Orth's  fluid 
gives  an  excellent  basis  for  a  hsematoxylin-eosin  stain  (see  (i),  p.  20.) 
The  fixative  should  always  be  freshly  prepared.  It  is  convenient  to 
keep  the  8-per-cent.  formalin  solution  and  the  double-strength 
Miiller's  fluid  in  stock.  Orth's  fluid  is  then  prepared  by  simply  tak- 
ing equal  parts  of  each. 

(6)  Osmic  Acid. — This,  in  a  i-per-cent.  aqueous  solution,  is  a 
quick  and  excellent  fixative  of  poor  penetrating  power.  Very  small 
pieces  of  tissue  must  therefore  be  used.  They  should  remain  in  the 
fluid  from  twelve  to  twenty-four  hours.  Osmic  acid  stains  fat  and 
myelin  black  and  is  consequently  useful  in  demonstrating  their 
presence  in  tissues.     Fixation  should  take  place  in  the  dark. 

(7)  Flemming's  Fluid. 

Chromic  acid,  i-per-cent.  aqueous  solution,  25  c.c. 

Osmic  acid,  i-per-cent.  aqueous  solution,  10  c.c. 

Glacial  acetic  acid,  i-pcr-ccnt.  aqueous  solution,  10  c.c. 

Water,  55  c.c. 


8  HISTOLOGICAL  TECHNIC 

Flemming's  fluid  is  one  of  the  best  fixatives  for  nuclear  structures, 
and  is  of  especial  value  in  demonstrating  mitotic  figures.  Very- 
small  pieces  of  tissue  should  be  placed  in  the  fixative,  where  they 
remain  for  from  twenty-four  hours  to  three  days.  The  solution 
should  be  freshly  made  as  required,  or  a  stock  solution  without  the 
osmic  acid  may  be  kept,  and  the  latter  added  at  the  time  of  using. 

(8)  Mercuric  Chlorid. — This  may  be  used  either  in  saturated 
aqueous  solution  or  in  saturated  solution  in  0.75-per-cent.  salt  solu- 
tion. Fixation  is  complete  in  from  twelve  to  twenty-four  hours, 
and  is  usually  very  satisfactory. 

A  saturated  solution  of  mercuric  chlorid  in  5-per-cent.  aqueous 
solution  of  glacial  acetic  acid  also  gives  good  results. 

(9)  Zenker's  Fluid. 

Potassium  bichromate,  2 .  5  gm. 

Sodium  sulphate,  i .  o  gm. 

Mercuric  chlorid,  5.0  gm. 

Glacial  acetic  acid,  S .  o  c.c. 

Water,  100. o  c.c. 

This  fluid  should  be  freshly  made,  or  the  salts  may  be  kept  in  solution 
and  the  acetic  acid  added  at  time  of  using. 

Zenker's  fluid  is  a  good  general  fij^ative,  but  usually  causes  some 
shrinkage  of  the  tissue  elements.  Fixation  requires  from  six  to 
twenty-four  hours.  The  most  serious  drawback  to  Zenker's  fluid 
is  the  fact  that  the  mercuric  chlorid  sometimes  produces  dark, 
irregular  precipitates  in  the  tissues.  This  may  be  remedied,  however, 
by  the  use  of  iodine  and  iodid  of  potassium  in  the  hardening  process 
(see  Hardening,  p.  9). 

(10)  Picric  acid  is  an  excellent  fixative  for  cytoplasm.  It  may  be 
used  in:  (a)  Saturated  aqueous  solution;  (b)  saturated  solution  of 
picric  acid  in  i-per-cent.  aqueous  solution  of  acetic  acid;  (c)  saturated 
solution  of  picric  acid  in  2-per-cent.  aqueous  solution  of  sulphuric 
acid. 

n.  Hardening 

Most  fixatives  are  also  hardening  agents  if  their  action  is  pro- 
longed. This  is,  however,  often  detrimental.  It  is,  therefore, 
customary,  after  fixation  is  complete,  to  carry  the  specimens,  with  or 
without  washing,  through  successively  stronger  grades  of  alcohol 
for  the  purpose  of  hardening  the  tissues.     For  general  histological 


GENER.^  TECHNIC  9 

purposes  the  specimens  may  be  transferred  directly  to  70-per-cent. 
or  80-per-cent.  alcohol,  which  should  be  changed  once  or  twice. 
In  the  case  of  delicate  tissues  the  first  grade  of  alcohol  should  be 
40-per-cent.  or  50-per-cent.,  the  second  70-per-cent.,  and  the  third 
80-per-cent.  The  specimens  should  remain  in  each  grade  from 
twelve  to  twenty-four  hours. 

Washing  the  tissues  after  fixation  is  not  a  matter  of  indifference. 
In  some  cases  water  should  be  used,  while  in  other  cases  water  is 
liable  to  undo  the  action  of  the  fLxative,  in  which  cases  alcohol  must 
be  used  for  washing. 

After  fixation  in  alcohol  no  washing,  of  course,  is  necessary. 
Specimens  fixed  in  strong  alcohol  are  embedded  immediately  (see 
Embedding,  p.  11),  or  preserved  (see  Preserving,  p.  9).  After 
fixation  in  dilute  alcohol  the  specimens  are  passed  through  the  graded 
alcohols  up  to  80-per-cent. 

After  fixation  in  formalin  solutions  the  specimens  are  passed 
directly  through  the  graded  alcohols  without  washing  in  water. 
Specimens  fixed  in  any  solution  containing  picric  acid  should  not  be 
washed  in  water,  but  passed  directly  through  the  alcohols;  and  it  is 
usually  necessary  to  change  each  grade  in  order  to  wash  out  the  picric 
acid. 

Specimens  fixed  in  osmic  acid  or  any  solution  containing  osmic 
acid  should  be  washed  in  running  water  before  being  passed  through 
the  graded  alcohols.  After  solutions  containing  potassium  bichro- 
mate the  specimens  should  be  washed  in  water  sufficiently  to  remove 
the  excess  of  bichromate,  though  too  prolonged  washing  seems  to  be 
detrimental.  A  precipitate  forms  in  the  alcohols,  but  this  apparently 
does  no  harm. 

After  mercuric  chlorid  or  Zenker  fixation  the  washing  may  be 
done  either  in  water  or  in  alcohol.  To  avoid  precipitates  in  the  tis- 
sues add  a  small  quantity  of  an  iodin  solution  (equal  parts  tincture 
iodin  and  lo-per-cent.  aqueous  solution  potassium  iodid)  to  any  of 
the  grades  of  alcohol.  As  the  alcohol  becomes  clear  more  of  the  solu- 
tion is  added  until  the  alcohol  remains  slightly  tinged. 

III.  Preserving 

Hardened  tissues  are  usually  preserved  in  80-pcr-ccnt.  alcohol. 
Formalin  in  aqueous  solutions  of  i-per-ccnt.  to  lo-per-ccnt.  is  also 
used  as  a  preservative.     In  either  case,  when  it  is  necessary  to  pre- 


10  HISTOLOGICAL  TECHNIC 

serve  the  specimens  for  a  considerable  length  of  time  (several  months 
or  longer),  the  tissues  are  hkely  to  lose  their  staining  qualities  to  a 
certain  extent.  Preserving  the  specimens  in  equal  parts  of  strong 
alcohol,  glycerin,  and  distilled  water  is  successful  as  a  partial  remedy 
for  this. 

IV.  Decalcifying 

Tissues  containing  lime  salts,  like  bones  and  teeth,  must  have 
the  lime  salts  dissolved  out  before  sections  can  be  cut.  This  process 
is  known  as  decalcification. 

Tissues  to  be  decalcified  must  be  firSt  fixed  and  hardened.  Fix- 
ation in  Orth's  fluid  and  hardening  in  graded  alcohols  give  good  re- 
sults. After  hardening,  the  tissue  is  washed  in  water  and  placed  in 
one  of  the  following  decalcifying  fluids.  The  quantity  of  fluid  should 
always  be  large  and  the  fluid  frequently  changed.  The  completion 
of  decalcification  can  be  determined  by  passing  a  needle  through 
the  specimen  or  by  cutting  it  with  a  scalpel.  The  time  required  varies 
with  the  size  and  hardness  of  the  specimen  and  the  decalcifying  fluid 
used.  When  decalcification  is  complete,  the  specimen  is  washed  in 
sufficient  changes  of  water  to  remove  all  trace  of  acid.  This  may  be 
quickly  accomplished  by  the  addition  of  a  little  ammonium  hydrate 
to  the  water.     The  specimen  is  then  carried  through  graded  alcohols. 

(i)  Hydrochloric  Acid. — This  may  be  used  in  aqueous  solutions 
of  from  0.5-per-cent.  to  5-per-cent.  A  very  satisfactory  decalcifying 
mixture  is  that  known  as  Ebner's  hydrochloric-salt  solution.  It 
consists  of: 

Sodium  chlorid,  saturated  aqueous  solution,  i  part. 

Water,  2  parts. 

Hydrochloric  acid,  sufficient  to  make  a  from  2-per-cent.  to  5- 
per-cent.  solution. 

The  addition  of  the  salt  prevents  swelling  of  the  tissue.  This  fluid 
is  slow  in  acting  and  should  be  changed  every  day. 

(2)  Nitric  Acid. — This  is  less  used  than  the  preceding.  The 
strength  should  be  from  i-per-cent  to  lo-per-cent.  aqueous  solution. 
Weak  solutions  (i-per-cent.  to  2-per-cent.)  will  decalcify  small  foetal 
bones  in  from  three  to  twelve  days.  For  larger  bones  stronger 
solutions  and  longer  time  are  required.  Transferring  from  the  nitric 
solution  to  a  5-per-cent.  alum  solution  for  twenty-four  hours  before 
washing  will  prevent  swelling  of  the  tissue.     Phloroglucin  is  some.- 


GENER.\L  TECHNIC  11 

times  added  to  the  nitric  acid  solution  for  the  purpose  of  protecting 
delicate  tissues  or  of  allowing  stronger  solutions  of  the  acid  to  be 
used.  One  gram  of  phloroglucin  is  dissolved  in  lo  c.c.  of  nitric  acid. 
To  this  are  added  loo  c.c.  of  lo-per-cent.  aqueous  solution  of  nitric 
acid.  Small  pieces  of  tissue  decalcify  in  a  few  hours.  If  less  rapid 
action  is  desired,  reduce  the  amount  of  nitric  acid  without  changing 
the  percentage  of  phloroglucin. 

(3)   Small  bones  may  be  satisfactorily  decalcified  in  Zenker's  fluid 
(see  Fixatives,  page  8),  or  in  the  following: 


Picric  acid. 

I  part. 

Chromic  acid, 

I  part. 

Glacial  acetic  acid, 

V.  Embedding 

S  parts, 

Most  hardened  tissues  are  still  not  firm  enough  to  be  cut  into  the 
thin  sections  suitable  for  microscopic  study.  In  order  to  support  the 
tissue  elements  and  render  them  more  firm  for  section  cutting,  re- 
course is  had  to  embedding.  This  consists  in  impregnating  the 
tissues  with  some  substance  which  is  liquid  when  the  tissues  are  placed 
in_it,  but  which  can  be  made  to  solidify  throughout  the  tissues.  In 
this  way  the  tissue  elements  are  held  firmly  in  place.  The  embedding 
substances  most  used  are  celloidin  and  paraffin. 

Celloidin  Embedding 

(i)  Alcohol-ether  Celloidin. — Two  solutions  should  be  made. 

Solution  No.  2.  Thick  celloidin — a  5-per-cent.  solution  of  cel- 
loidin in  equal  parts  96-per-cent.  alcohol  and  ether. 

Solution  No.  i.  Thin  celloidin — made  by  diluting  solution  No.  2 
with  an  equal  volume  of  equal  parts  of  alcohol  and  ether. 

The  hardened  tissues  are  placed  successively  in: 

Strong  alcohol  (96-per-cent.)  twelve  to  twenty-four  hours,  to 
dehydrate. 

Equal  parts  alcohol  and  ether,  twelve  to  twenty-four  hours. 

Thin  celloidin,  twenty-four  hours  to  several  days. 

Thick  celloidin,  twenty-four  hours  or  longer. 

The  exact  time  tissues  should  remain  in  the  different  grades  of 
celloidin  depends  upon  the  character  of  the  tissue,  the  size  of  the 
specimen,  and  the  thinness  of  section  desired.  Many  tissues  may  be 
advantageously  left  for  weeks  in  thin  celloidin. 


12  HISTOLOGICAL  TECHNIC 

The  specimen  must  now  be  "blocked"  and  the  celloidin  hardened. 
By  blocking  is  meant  fastening  the  specimen  impregnated  with  cel- 
loidin to  a  block  of  wood  or  other  suitable  material  which  may  be 
clam.ped  in  the  microtome  (see  Section  Cutting,  p.  14).  The  specimen 
may  be  taken  from  the  thick  celloidin  (considerable  of  the  latter 
adhering  to  the  specimen),  quickly  pressed  upon  a  block  of  wood  or 
vulcanized  fibre,  allowed  to  harden  five  to  ten  minutes  in  air,  and  then 
immersed  in  80-per-cent.  alcohol.  The  alcohol  gives  an  even  hard- 
ening of  the  celloidin,  attaching  the  specimen  firmly  to  the  block. 
Another  method,  and  one  by  which  very  even-shaped  blocks  may  be 
obtained,  is  to  place  the  specimen  from  the  thick  celloidin  into  a  little 
paper  box  (made  by  folding  paper  over  a  wooden  block),  sUghtly 
larger  than  the  specimen,  and  covering  with  thick  celloidin.  The 
celloidin  should  dry  slowly  under  a  bell-jar  for  from  two  to  twelve 
hours,  according  to  the  amount  of  celloidin,  after  which  it  should  be 
immersed  in  80-per-cent.  alcohol  and  the  paper  pulled  off.  Such  a 
block  may  be  cut  into  any  desired  shape.  It  is  attached  to  the 
wooden  or  vulcanized  block  by  dipping  for  a  moment  in  thick  celloidin, 
and  then  pressing  firmly  down  upon  the  block.  After  five  to  ten 
minutes'  drying  in  air  it  is  transferred  to  80-per-cent.  alcohol. 

Old,  hard,  celloidin-embedded  specimens  are  sometimes  difficult 
to  attach  to  blocks.  This  usually  may  be  accompKshed  by  first 
thoroughly  drying  the  specimen  and  then  dipping  it  in  equal  parts 
alcohol  and  ether  for  a  few  minutes.  This  softens  the  surface  of  the 
celloidin,  after  which  the  specimen  is  dipped  in  thick  celloidin  and 
blocked.  Embedded  or  blocked  specimens  can  be  kept  in  80-per- 
cent.  alcohol.  After  several  months,  however,  the  celloidin  is  likely 
to  become  too  soft  for  good  section  cutting.  In  that  case  the  speci- 
mens can  be  readily  re-embedded  by  dissolving  out  the  old  celloidin 
with  alcohol  and  ether  and  putting  them  again  through  the  regular 
embedding  process. 

(2)  Clove-oil  Celloidin. — A  more  rapid  impregnation  of  the 
tissue  may  be  obtained  by  means  of  what  is  known  as  clove-cil  cel- 
loidin. 

Celloidin,  30  gm. 

Clove  oil,  100  c.c. 

Ether,  400  c.c. 

Alcohol,  absolute,  20  c.c. 

The  celloidin  is  first  placed  in  a  jar  and  the  clove  oil  and  ether  added. 
From  two  to  four  days  are  required  for  solution  of  the  celloidin. 


GENERAL  TECHNIC  13 

During  this  time  the  jar  should  be  shaken  several  times.  After  the 
celloidin  is  dissolved  the  absolute  alcohol  is  added  and  the  solution 
is  ready  for  use. 

The  specimen  must  be  thoroughly  dehydrated,  placed  in  alcohol 
and  ether  or  pure  ether  for  a  few  hours,  and  then  transferred  to  the 
clove-oil  celloidin.  From  six  to  twelve  hours  is  sufficient  to  impreg- 
nate small  pieces  of  tissue.  The  tissue  is  now  taken  from  the  cel- 
loidin, placed  directly  upon  a  wooden  or  vulcanized  block,  and  im- 
mersed in  chloroform.  The  celloidin  hardens  in  about  an  hour,  and 
is  then  ready  for  sectioning.  The  specimen  is  very  firm,  and  very 
thin  sections  can  be  cut. 

A  disadvantage  in  clove-oil  celloidin  is  that  neither  the  blocks  nor 
the  sections  can  be  kept  permanently  in  alcohol,  as  can  those  embedded 
in  alcohol-ether  celloidin.  They  may,  however,  be  kept  for  several 
weeks  in  pure  chloroform. 

Paratfin  Embedding 

For  paraffin  embedding  a  thermostat  or  parafiSn  oven  is  necessary 
in  order  that  a  constant  temperature  may  be  maintained.  The  tem- 
perature should  be  about  56°  C.  Pure  parafi&n,  the  melting-point 
of  which  is  from  50°  to  55°  C,  is  used.  In  very  warm  weather  it 
may  be  necessary  to  add  to  this  a  little  paraffin,  the  melting-point  of 
which  is  62°  C. 

The  hardened  tissue  is  first  put  in  96-per-cent.  alcohol  for  from 
twelve  to  twenty-four  hours,  and  then  completely  dehydrated  by  put- 
ting in  absolute  alcohol  for  the  same  length  of  time,  or  less  for  small 
specimens.  It  is  then  transferred  to  some  solvent  of  paraffin. 
Some  of  the  solvents  used  are  xylol,  oil  of  cedarwood,  chloroform,  and 
toluol.  Of  these  the  best  are  perhaps  xylol  and  oil  of  cedarwood. 
The  tissue  should  remain  in  either  of  these  for  several  hours,  or  until 
the  tissue  becomes  more  or  less  transparent.  It  is  then  placed  in 
melted  paraffin,  in  the  paraffin  oven,  for  from  one  to  three  hours, 
according  to  the  size  and  density  of  the  specimen.  This  allows 
the  tissues  to  become  impregnated  with  the  melted  parafiin.  The 
paraffin  should  be  changed  twice. 

In  case  of  very  delicate  tissues  it  is  well  to  transfer  them  from 
the  absolute  alcohol  to  a  mixture  of  equal  parts  absolute  alcohol  and 
xylol  for  a  short  time  before  putting  them  into  the  pure  xylol.  In  the 
same  way  a  mixture  of  equal  parts  xylol  and  paraffin  may  be  used 
before  putting  the  tissues  into  pure  paraffin. 


14  HISTOLOGICAL  TECHNIC 

For  hardening  the  parafhn  in  and  around  the  tissue  a  very  con- 
venient apparatus  consists  of  a  plate  of  glass  and  several  L-shaped 
pieces  of  iron  or  lead.  Two  of  these  are  placed  on  the  glass  plate  in 
such  a  manner  as  to  enclose  a  space  of  the  desired  size.  Into  this  are 
placed  the  specimen  and  sufficient  melted  paraffin  to  cover  it.  Both 
glass  and  irons  should  be  smeared  with  glycerin  to  prevent  the  par- 
affin from  adhering,  and  should  be  as  cold  as  possible,  so  that  the  par- 
affin may  harden  quickly.  The  same  paper  boxes  described  under 
celloidin  embedding  may  also  be  used  for  paraffin.  Another  good 
method  for  small  pieces  of  tissue  is  to  place  the  specimen  in  paraffin 
in  an  ordinary  watch-glass  which  has  been  coated  with  glycerin. 
Both  paper-box  and  watch-glass  specimens  are  immersed  in  cold 
water  as  soon  as  the  surface  of  the  paraffin  has  become  hard.  After 
the  paraffin  has  hardened  any  excess  may  be  cut  away  with  a  knife. 

Paraffin-embedded  specimens  may  be  kept  indefinitely  in  air. 
For  section  cutting,  the  block  of  paraffin  is  attached  to  a  block  of 
wood  or  of  vulcanite  or  to  the  metallic  block-holder  of  the  microtome. 
This  is  done  by  heating  the  block-holder,  pressing  the  paraffin  block 
firmly  upon  it,  and  then  dipping  the  whole  into  cold  water. 


VI.  Section  Cutting 

The  older  method  of  making  free-hand  sections  with  a  razor  has 
been  almost  completely  superseded  by  the  use  of  a  cutting  instru- 
ment known  as  the  microtome.  This  consists  essentially  of  a  clamp 
for  holding  the  specimen  and  a  microtome  knife  or  razor.  The  two 
are  so  arranged  that  when  knife  and  specimen  meet,  a  section  of  any 
desired  thickness  may  be  cut. 

The  technic  of  section  cutting  differs  according  to  whether  the 
specimen  is  embedded  in  celloidin  or  in  paraffin. 

In  cutting  celloidin  sections  the  knife  is  so  adjusted  that  it  passes 
obliquely  through  the  specimen,  as  much  as  possible  of  the  cutting 
edge  being  used.  The  knife  is  kept  flooded  with  8o-per-cent.  alcohol 
and  the  specimens  are  removed  by  means  of  a  camel' s-hair  brush  to  a 
dish  of  8o-per-cent.  alcohol,  where  they  may  be  kept  for  some  time 
if  desired.  When  celloidin  sections  tear  or  when  very  thin  sections 
are  desired  it  is  often  of  advantage  to  paint  the  surface  of  the  block, 
after  cutting  each  section,  with  a  coat  of  very  thin  celloidin. 

Celloidin  sections  are  usually  not  thinner  than  lo/x,  although 


GENER.\L  TECHNIC  15 

under  favorable  conditions  sections  5//^  or  even  3/-«  in  thickness  may 
be  obtained. 

In  cutting  paraffin  sections  the  knife  is  kept  dry  and  is  passed 
not  obliquely  but  straight  through  the  specimen,  only  a  small  part  of 
the  cutting  edge  being  used.  An  exception  is  made  in  the  case  of  very 
large  parafhn  sections,  where  an  oblique  knife  is  used.  Sections  are 
removed  from  the  knife  by  a  dry  or  slightly  moistened  brush.  If  not 
desired  for  immediate  use  the  sections  may  be  conveniently  kept  for  a 
short  time  on  a  piece  of  smooth  paper.  If  sections  curl  they  may  be 
flattened  by  floating  on  warm  30-per-cent.  alcohol  or  on  warm 
water. 

Paraffin  sections  may  be  so  cut  that  the  edges  of  the  sections  ad- 
here. Long  series  or  "ribbons"  of  sections  may  thus  be  secured. 
This  is  of  decided  advantage  when  serial  sections  are  desired.  Fail- 
ure of  the  secticns  to  cut  evenly  or  to  adhere  in  ribbons  is  usually  due 
to  the  paraffin  being  too  hard  and  brittle,  which  of  course  is  due  to  its 
low  temperature.  If  much  section  cutting  is  to  be  done,  the  operator 
will  find  himself  amply  repaid  by  having  the  room-temperature  fairly 
high.  In  case  paraffin  of  a  melting-point  of  50°  to  55°  C.  is  used,  a 
room  temperature  of  73°  to  75°  F.  will  greatly  facihtate  the  work. 
Where  it  is  not  possible  to  have  a  high  room  temperature,  recourse 
may  be  had  to  coating  the  surface  of  the  block  with  a  paraffin  of  lower 
melting-point  than  that  used  for  the  embedding.  A  similar  effect 
may  be  obtained  by  holding  a  heated  metal  plate  or  bar  near  the 
block  until  the  paraffin  is  slightly  softened.  This  process  may  be  re- 
peated as  often  as  necessary. 

In  addition  to  the  fact  that  ribbon  series  can  be  cut  in  paraffin, 
this  embedding  substance  also  has  the  advantage  over  celloidin  that 
thinner  sections  can  be  obtained.  On  the  other  hand,  celloidin  em- 
bedding produces  less  shrinkage  of  the  tissues  than  paraffin  embedding 
with  the  accompanying  heat. 

Frozen  Sections. — This  method,  while  more  used  in  pathology 
where  rapid  diagnosis  is  more  often  important,  is  still  sometimes 
extremely  useful  to  the  histologist,  especially  as  an  easy  and  quick 
method  of  testing  material.  Perfectly  fresh  tissues  may  be  used  or 
tissues  which  have  been  previously  fixed.  Fixed  tissues  must  have 
the  fixative  thoroughly  removed  before  freezing.  Of  fixatives  10- 
per-cent.  formalin  is  probably  the  best  and  the  tissue  should  remain  in 

*  H  =micromiUimetcr  or  micron  =  ,  ,}(,<,  of  a  milli meter  =  microscopic  unit  of  measure 
■«  about  j.'jioo  ^^f  '^^  inch. 


16  HISTOLOGICAL  TECHNIC 

the  fixative  from  one  to  two  hours.  If  time  is  important  the  tissue 
may  be  boiled  for  two  or  three  minutes  in  the  formalin  solution. 

Ether,  rhigolene  and  carbon  dioxid  are  the  most  common  freezing 
agents.  A  special  freezing  microtome  and  knife  may  be  used,  or  a 
freezing  attachment  may  be  used  with  the  ordinary  microtome.  In 
ether  freezing  the  ether  is  vaporized  by  means  of  compressed  air  and 
the  vapor  carried  to  the  under  side  of  a  metalHc  plate  upon  which  the 
block  of  tissue  is  placed.  In  carbon  dioxid  freezing,  which  has  now 
largely  superseded  ether  freezing  on  account  of  convenience  and  econ- 
omy, the  commercial  cylinder  of  gas  such  as  is  used  for  charging  soda 
fountains  is  used.  As  the  liquid  carbon  dioxid  and  not  the  gas  is 
required  for  freezing,  the  cylinder  should  be  hung  valve  end  down, 
with  the  valve  about  the  level  of  the  microtome.  The  carbon  dioxid 
is  carried  to  the  metallic  disc  of  the  microtome  by  means  of  a  stout 
rubber  tube  and  it  is  advisable  to  screw  a  cap  with  a  small  hole  in  it 
over  the  valve  and  to  attach  a  longer  handle  to  the  valve  lever  in  order 
to  more  perfectly  control  the  flow.  The  piece  of  tissue  to  be  frozen 
should  not  be  over  5  mm-  thick  and  the  freezing  should  be  done 
slowly.  A  proper  hardness  of  the  tissue  is  important  and  is  of  course 
determined  by  the  amount  of  carbon  dioxid  admitted. 

As  the  frozen  section  is  not  supported  by  any  embedding  mass, 
special  handling  is  required,  the  section  being  attached  to  a  slide 
or  cover-glass  before  staining.  For  this  purpose  either  egg  albumen 
or  celloidin  may  be  used. 

Egg  albumen,  50  c.c. 

Distilled  water,  150  c.c. 

Saturated  solution  sodium  salicylate  (made 
slightly  alkaline  with  lithium  carbonate)  50  c.c. 

(or  sufficient  to  completely  dissolve  the  albumen). 

Sections .  from  material  previously  fixed  are  transferred  directly 
from  the  microtome  to  the  albumen  solution.  Sections  from  fresh 
material  are  placed  for  three  to  five  minutes  in  5-  to  lo-per-cent. 
formalin  solution  before  being  transferred  to  the  albumen  solution. 

From  the  albumen  solution  sections  are  floated  on  a  slide  or 
cover-glass,  the  excess  of  solution  drained  off  and  the  section  firmly 
blotted  with  several  thicknesses  of  washed  cheese-cloth.  The  slide 
or  cover-glass  is  next  immersed  in  alcohol  or  in  equal  parts  alcohol 
and  ether  to  coagulate  the  albumen,  thus  fixing  the  section  to  the 
glass.  The  section  may  now  be  stained  and  mounted  in  the  usual 
way 


GENERAL  TECHNIC  17 

In  the  celloidin  method  the  section  is  transferred  from  the  micro- 
tome to  water,  floated  upon  a  sHde,  blotted  with  filter  paper,  flooded 
with  absolute  alcohol  and  drained.  Before  the  alcohol  dries  the 
slide  is  flooded  with  a  very  thin  celloidin  solution  which  is  immediately 
drained  off.  The  celloidin  is  then  allowed  to  harden  a  moment 
and  the  slide  immersed  in  water.  The  section  is  now  fixed  to  the 
slide  and  may  be  stained  and  mounted  as  usual. 

VII.  Staining 

This  is  for  the  purpose  of  more  readily  distinguishing  the  different 
tissue  elements  from  one  another  by  their  reactions  to  certain  dyes. 

Based  upon  their  action  upon  the  different  tissue  elements,  stains 
may  be  classified  as  (i)  nuclear  dyes,  which  stain  nuclear  structures; 
and  (2)  plasma  dyes,  which  stain  the  cell  body  or  cytoplasm.  Plasma 
dyes,  also,  as  a  rule,  stain  the  intercellular  tissue  elements,  and  are 
therefore  known  as  diffuse  stains. 

The  dyes  most  frequently  used  for  staining  tissues  are : 

I.  Nuclear  dyes:  (a)  Haematoxylin  and  its  active  principle, 
hasmatein;  (b)  carmine  and  its  active  principle,  carminic  acid;  (c) 
basic  aniUne  dyes. 

II.  Plasma  dyes:  (a)  Eosin;  (b)  neutral  carmine,  (c)  picric  acid; 
(d)  acid  aniline  dyes. 

I.  Nuclear  Dyes. — (a)  Hematoxylin. 

1.  Gage's  Hcematoxylin. 

Ammonia  or  potash  alum,  7 . 5  gm. 

Distilled  water,  200.0  c.c. 

Boil  for  10  minutes  to  sterilize;  cool  and  add  the  following 
solution: 

Haematoxylin  crystals,  o.i  gm. 

Alcohol  9S-pcr-cent.,  10. o  c.c. 

Four  grams  chloral  hydrate  are  then  added  to  the  mixture 
to  prevent  growth  of  germs. 

This  dye  may  be  used  in  full  strength  or  diluted  with  alum  water. 
It  stains  in  from  two  to  five  minutes. 

2.  Delafield's  IIcBmatoxylin. 


Ifa;matoxylin  crystals, 

I  gm. 

Alcohol, 

6  c.c. 

Ammonia  alum,  saturated  aqueous  solution, 
2 

100  c.c. 

18  HISTOLOGICAL  TECHNIC 

The  hsematoxylin  should  be  first  dissolved  in  the  alcohol  and  then 
added  to  the  alum  solution.  The  mixture  should  next  be  allowed  to 
stand  in  the  light  for  from  seven  to  ten  days  to  ripen.  It  is  then 
filtered,  and  to  the  filtrate  are  added: 

Glycerin,  25  c.c. 

Wood  naphtha,  25  c.c. 

The  mixture  is  again  allowed  to  stand  for  from  two  to  four  days  and 
filtered.  It  may  be  used  full  strength  or  diluted  with  equal  parts  of 
water.     It  stains  in  from  two  to  five  minutes. 

3.  Heidenhain's  Hcematoxylin. 

Hcematoxylin  crystals,  i  gm. 

Water,  100  c.c. 

Sections  are  first  placed  for  from  four  to  eight  hours  in  a  2.5-per-cent. 
aqueous  solution  of  ammonium  sulphate  of  iron.  They  are  then 
washed  in  water  and  transferred  to  the  haematoxylin  solution  until 
they  are  intensely  blue  or  black  (usually  several  hours).  The  sec- 
tions are  now  washed  in  water  and  differentiated  by  again  placing 
in  the  iron  solution  till  they  have  a  light  grayish  color.  After  this 
they  are  thoroughly  washed  in  water. 

4.  Mayer's  Hmmalum. 

Hsematein,  i  gm. 

Alcohol,  50  c.c. 

Ammonia  alum,  5-per-cent.  aqueous  solution,  1,000  c.c. 

The  h^ematein  is  first  dissolved  in  the  alcohol,  after  which  the  alum 
is  added.  This  dye  does  not  require  any  ripening,  and  is  thus  avail- 
able for  immediate  use.  It  is  a  rapid  nuclear  dye  usually  requiring 
not  more  than  from  three  to  five  minutes. 

5.  A  combination  of  Gage's  and  Mayer's  formulee  makes  a  very 
satisfactory  nuclear  dye. 

Haematein,  5  gm. 
Alcohol,  50  c.c. 
Chloral  hydrate,  20  gm. 
Ammonia  alum,  5-per-cent.  aqueous  solution  (steril- 
ized), 1,000  c.c. 

The  haematein  is  first  dissolved  in  the  alcohol  and  then  added  with 
the  chloral  hydrate  to  the  alum  solution.  This  solution  is  used  in 
full  strength  and  stains  in  from  three  to  five  minutes. 


GEXER.\L  TECHNIC  19 

6.  Weigerfs  HcBmatoxylin. 

Two  stock  solutions  should  be  made  up  as  follows: 

A.  i-per-cent.  hjematoxylin,  in  Q6-per-cent.  alcohol. 

B.  Hydrochloric  acid  (sp.  gr.  1.126),  10  c.c. 
Ferric  chloride,  30-per-cent.,  40  c.c. 
Distilled  water,  950  c.c. 

For  use,  mix  equal  parts  of  A  and  B.  The  mixture  will  keep  two  or 
three  days.  This  is  a  rapid  stain  usually  requiring  not  mere  than  a 
minute.  A  more  brilliant  nuclear  stain  may  be  obtained  by  over- 
staining  and  then  decolorizing.  After  the  stain  wash  the  sections 
in  water  and  then  decolorize  to  the  pioper  degree  in  weakly  acidu- 
lated water.  To  step  the  action  of  the  acid  the  sections  should  be 
dipped  in  water  made  slightly  alkaline  with  ammonia.  This  is  an 
excellent  stain  and  gives  brilliant  results.  It  is  especially  good  in 
cases  where  the  material  has  become  old  and  lost  its  affinity  for  ordi- 
nary haematoxylin  stains. 
{h)  Alum-carmine. 

Carmine,  2  gifi. 

x\lum,  5  gm. 

Carbolic  acid,  .                     .                                                2  gm. 

Water,  100  c.c. 

The  alum  is  first  dissolved  in  the  100  c.c.  of  warm  distilled  water, 
after  which  the  carmine  is  added.  This  mixture  is  then  boiled  for 
twenty  minutes,  allowed  to  cool,  and  filtered.  The  carbolic  acid  is 
then  added.     This  is  a  slow-acting  pure  nuclear  dye. 

(c)  Basic  Aniline  Dyes — gentian  violet,  methyl  violet,  methyl 
green,  methyl  blue,  toluidin  blue,  fuchsin,  thionin,  safranin,  etc. 

These  are  best  kept  in  stock  in  saturated  alcoholic  solutions. 
WTien  desired  to  use,  a  few  drops  of  the  alcoholic  solution  are  added 
to  distilled  water.  No  rule  as  to  exact  proportions  can  be  given,  as 
these  depend  upon  the  material,  the  fixation,  and  the  intensity  of 
stain  desired. 

II.  Plasma  Dyes. — (a)  Eosin. 

This  is  prepared  as  follows:  Water-soluble  eosin  is  dissolved  in 
water  to  saturation.  It  is  then  precipitated  by  hydrochloric  acid 
and  the  precipitate  washed  with  water  upon  a  lilter  until  the  filtrate 
is  tinged  with  eosin.  After  drying,  the  precipitate  is  dissolved  in 
strong  alcohol,  i  gm.  of  eosin  to  1,500  c.c.  of  alcohcl,  or  water- 
soluble  eosin  may  be  kept  in  saturated  aqueous  solution  containing 


20  HISTOLOGICAL  TECHNIC 

a  trace  of  thymol  as  a  preservative.  This  may  be  diluted  to  any 
desired  strength  at  time  of  using.     Eosin  is  a  rapid  plasma  stain. 

(b)  Neutral  Carmine. 

Carmine,  i  gm. 

Liquor  ammonii  caustici,  5  c.c. 

Distilled  water,  50  c.c. 

The  last  two  ingredients  are  first  mixed,  and  the  carmine  then  added. 
This  solution  is  allowed  to  remain  in  an  open  vessel  for  about  three 
days,  or  until  the  odor  of  ammonia  has  disappeared,  after  which  it 
is  filtered. 

(c)  Picric  Acid — used  mainly  as  the  plasma-staining  element  of 
such  a  staining  mixture  as  picro-acid-fuchsin. 

(d)  Acid  Aniline  Dyes. — Of  these,  acid  fuchsin,  erythrosin,  and 
orange  G  are  most  used.  They  may  be  prepared  and  kept  in  stock 
in  the  same  manner  as  the  basic  aniline  dyes  (see  above).  Erythrosin 
is  of  especial  value  for  sections  which  take  the  eosin  stain  poorly. 

Staining  Sections 

It  is  often  of  advantage  to  stain  the  different  tissue  elements  dif- 
ferent colors.  This  may  be  accomphshed  either  by  staining  suc- 
cessively with  several  dyes,  or  by  a  single  staining  with  a  mixture 
of  dyes.     The  following  are  the  methods  in  most  common  use: 

(i)  Staining  Double  with  Hematoxylin  and  Eosin. — Sec- 
tions are  first  washed  in  water.  They  are  then  stained  with  haema- 
toxyhn  (solutions  i,  2,  4,  5,  or  6,  pp.  17-19)  from  one  to  five  minutes. 
After  being  thoroughly  washed  in  water,  they  are  dehydrated  in 
strong  alcohol  and  transferred  to  the  alcoholic  eosin  solution  (page 
19).  Most  sections  stain  in  from  two  to  five  minutes.  By  this 
method  nuclei  are  stained  blue  or  purple,  cell  bodies  and  intercellular 
substances  red. 

Very  often  a  more  brilliant  staining  may  be  accomplished  as 
follows:  Overs  tain  in  haematoxylin  and  wash  thoroughly  in  water; 
decolorize  in  water  slightly  acidulated  (8  or  10  drops  of  hydrochloric 
acid  to  100  c.c.  of  water)  until  only  the  nuclei  retain  the  stain;  wash 
in  water  which  has  been  made  slightly  alkaline  with  ammonium  hy- 
drate; then  stain  with  eosin  as  usual. 

(2)  Staining  with  Picro-acid-fuchsin. 

Acid-fuchsin,  i-per-cent.  aqueous  solution,  5  c.c. 

Picric  acid,  saturated  aqueous  solution,  100  c.c. 


GENERAL  TECHNIC  21 

This  solution  usually  stains  in  from  one  to  three  minutes.  Occa- 
sionally a  longer  staining  is  required.  Cell  bodies  including  muscle 
cells  and  fibres  are  stained  yellow  by  the  picric  acid,  connective- 
tissue  fibres  red  by  the  fuchsin.  After  staining,  the  sections  are 
washed  in  distilled  water. 

(3)  Triple  Staining  with  Hematoxylin  and  Picro-acid- 
FUCHSiN. — This  is  the  same  as  the  preceding  except  that  before  stain- 
ing with  picro-acid-fuchsm,  the  sections  are  overstained  in  heema- 
toxylin  (solutions  i,  2,  4,  5,  or  6,  pp.  17-19).  The  usual  purple  of 
haematoxyhn-stained  nuclei  is  changed  to  brown  by  the  action  of  the 
picric  acid.  Care  should  be  taken  that  the  sections  do  not  remain 
too  long  in  the  picro-acid-fuchsin,  or  the  haematoxylin  may  be  com- 
pletely removed.  After  staining,  sections  are  washed  in  distilled 
water  and  transferred  to  96-per-cent.  alcohol. 

If  sections  overstain  with  fuchsin,  the  staining  solution  may  be 
diluted  with  water;  if  sections  are  understained  with  fuchsin,  more 
fuchsin  may  be  added.  If  the  picric-acid  stain  is  not  sufficiently 
intense,  the  96-per-cent.  alcohol  should  be  tinged  with  picric  acid. 

(4)  Staining  with  Picro-carmine. 

Ammonium  carminate,  i  gm. 

Distilled  water,  35  c.c. 

Picric  acid,  saturated  aqueous  solution,  15  c.c. 

The  ammonium  carminate  is  first  dissolved  in  the  water,  after  which 
the  saturated  aqueous  solution  of  picric  acid  is  added  with  constant 
stirring.  The  mixture  is  then  allowed  to  stand  in  an  open  vessel  for 
two  days,  when  it  is  filtered.  This  fluid  stains  nuclei  and  connective 
tissue  red,  cell  protoplasm  yellow. 

Staining  in  Bulk 

By  this  is  meant  the  staining  of  blocks  of  tissue  before  cutting 
into  sections.  The  method  is  much  less  used  than  formerly.  It  is 
slower  than  section  staining  and  more  difficult  to  control.  Blocks  of 
the  hardened  tissue  are  transferred  to  the  stain  from  water  or  alcohol 
according  to  the  solvent  of  the  stain.  Alum-carmine  and  borax- 
carmine  are  the  most  used  general  l)ulk  stains. 

(i)  Alum-carmine. 

Carmine,  0.5  to  i  gm. 

Ammonia  alum,  4-pcr-ccnt.  aqueous  solution,  100  c.c. 


22  HISTOLOGICAL  TECHNIC 

After  mixing  the  ingredients,  the  solution  should  be  boiled  fifteen 
minutes,  and  after  cooling,  enough  sterile  water  added  to  replace  that 
lost  by  evaporation.  The  time  required  for  staining  depends  upon 
the  size  of  the  specimen.  There  is,  however,  little  danger  of  over- 
staining.  After  washing  out  the  excess  of  stain  with  water  the  speci- 
men is  dehydrated  and  embedded  in  the  usual  way. 
(2)  Borax-carmine,  Alcoholic  Solution. 

Carmine,  3  gm. 

Borax,  4  gm. 

Water,  93  c.c. 

After  mixing  the  above,  add  100  c.c.  70-per-cent  alcohol, 
allow  the  mixture  to  settle,  then  filter. 

About  twenty-four  hours  is  required  to  stain  blocks  0.5  cm.  in 
diameter.     Larger  blocks  require  longer  staining. 

Vm.  Mounting 

It  is  usually  desirable  to  make  permanent  preparations  or 
"mounts"  of  the  stained  specimens. 

The  most  satisfactory  media  for  mounting  specimens  are  glycerin 
and  Canada  balsam. 

(i)  Glycerin. — Sections  may  be  transferred  to  glycerin  from 
either  water  or  alcohol.  In  the  case  of  double-stained  specimens — 
hsematoxylin-eosin — the  glycerin  should  be  tinged  with  eosin,  as  the 
pure  glycerin  abstracts  the  eosin  from  the  tissues.  In  many  cases 
satisfactory  eosin  staining  may  be  obtained  by  simply  placing  the 
hsematoxyHn-stained  specimens  in  glycerin  strongly  tinged  with 
eosin  (eosin-glycerin) .  The  specimen  in  a  drop  of  glycerin  is  trans- 
ferred to  the  glass  mounting  slide,  the  excess  of  glycerin  removed  with 
filter  paper  or  with  a  pipette,  and  a  cover-glass  put  on. 

Glycerin  mounts,  as  a  general  rule,  are  unsatisfactory.  Further- 
more, they  must  be  cemented  to  exclude  the  air.  This  can  be  done 
by  painting  a  ring  of  gold-size,  or  a  thick  solution  of  gum  shellac  in 
alcohol  to  which  a  Httle  castor  oil  has  been  added,  around  and  over 
the  edge  of  the  cover-glass.  Both  cover-glass  and  slide  must  be 
cleaned  free  from  glycerin  before  the  cement  is  appHed.  A  cam.ers- 
hair  brush  moistened  with  alcohol  is  the  best  means  of  removing  the 
excess  of  glycerin. 

Glycerin  jelly  is  a  more  satisfactory  mounting  medium  than  pure 
glycerin.     It  can  be  purchased  from  firms  dealing  in  microscopical 


GENERAL  TECHNIC  23 

supplies  and  needs  merely  the  application  of  heat  to  make  it  fluid. 
Specimens  can  then  be  mounted  in  it  in  the  usual  manner,  and  after 
being  allowed  to  cool,  do  not  require  cementing. 

(2)  Balsam. — This  is  the  most  satisfactory  general  mounting 
medium.  It  has  an  advantage  over  glycerin  in  drying  down  perfectly 
hard  and  thus  needing  no  cement,  and  in  preserving  colors  more 
permanently.  Its  disadvantage  is  that  its  refractive  index  is  so 
high  that  it  sometimes  obscures  the  finer  details  of  structure,  espe- 
cially of  unstained  or  slightly  stained  specimens. 

Specially  prepared  Canada  balsam  is  dissolved  either  in  xylol 
or  in  oil  of  cedar,  the  solution  being  made  of  any  desired  consistence. 
Xylol-balsam  dries  much  more  quickly  than  does  the  oil-of-cedar 
balsam. 

Preparatory  to  mounting  in  balsam,  stained  sections  must  be 
thoroughly  dehydrated  and  then  passed  through  some  medium 
which  is  miscible  with  both  alcohol  and  balsam.  This  medium, 
which  at  the  same  time  renders  the  section  transparent,  is  known 
as  a  clearing  medium.  For  celloidin  specimens  the  most  satisfactory 
are: 

(i)  Oil  of  origanum  Cretici. 

(2)  Carbol-xylol  (xylol,  100  c.c,  carboKc-acid  crystals,  22  gm.), 
followed  by  pure  xylol. 

(3)  Xylol  and  cajeput  oil,  equal  parts,  followed  by  pure  xylol. 

After  clearing,  the  section  is  transferred  by  means  of  a  section- 
lifter  to  a  glass  mounting  slide.  In  case  oil  of  origanum  is  used,  it 
is  then  blotted  firmly  with  filter  paper  to  remove  the  excess  of  oil. 
Care  must  be  taken  to  have  the  filter  paper  several  layers  thick  in 
order  that  the  oil  may  be  completely  removed.  The  specimen  should 
also  be  blotted  firmly,  giving  the  oil  time  to  soak  into  the  paper. 
These  two  precautions  are  necessary  to  prevent  the  section  adhering 
to  the  paper  instead  of  to  the  shde.  After  blotting,  a  drop  of  balsam 
is  placed  upon  the  centre  of  the  specimen  and  a  cover-glass  put  on. 

When  xylol  is  used,  blotting  is  not  necessary.  Drain  off  the 
excess  of  oil,  put  a  droj)  of  balsam  on  the  specimen  and  put  on  a 
cover-g'ass. 

Paraffin  Sections. — The  technic  of  staining  and  mounting  paraffin 
sections  differs  from  that  of  celloidin  sections.  This  is  due  mainly  to 
the  fact  that  while  cellodin  is  transparent  and  may  remain  perma- 
nently in  the  specimen,  paraffin  is  opaque  and  must  be  dissolved  out 
before  the  section  is  fit  for  microscopic  study. 


24  HISTOLOGICAL  TECHNIC 

Bulk  staining  with  carmine  (page  21)  is  frequently  used  for  speci- 
mens which  are  to  be  embedded  in  parafi&n.  Sections  may  be  coun- 
terstained  if  desired. 

The  following  are  the  steps  to  be  followed  in  staining  and  mount- 
ing paraffin  sections : 

1.  To  attach  sections  to  slide: 

Place  a  drop  of  egg  albumen  (equal  parts  white  of  egg  and  glycerin 
to  which  a  little  carbolic  acid  may  be  added  for  preserving)  on  a 
slide,  and  spread  it  out  thin  with  the  finger. 

Place  a  few  drops  of  distilled  water  on  the  slide. 

Float  sections  on  the  water. 

Warm  gently  to  allow  sections  to  flatten — must  not  melt 
paraffin. 

Pour  off  excess  of  water,  holding  the  ends  of  the  ribbons  to  prevent 
them  floating  off. 

Stand  slides  on  end  a  few  hours  to  allow  water  to  evaporate. 

2.  To  remove  paraffin: 

Place  slide  in  xylol  three  to  five  minutes. 

3.  To  stain  sections: 

Place  slide  in  fresh  xylol  three  minutes. 

Transfer  to  absolute  alcohol. 

Transfer  to  gc-per-cent.  alcohol. 

Transfer  to  80-per-cent.  alcohol. 

Transfer  to  "50-per-cent.  alcohol.     (May  be  omitted.) 

Transfer  to  water. 

Stain  with  an  aqueous  stain. 

Wash  in  water. 

Transfer  to  50-per-cent.  alcohol.      (May  be  omitted.) 

Transfer  to  80-per-cent.  alcohol. 

Transfer  to  90-per-cent.  alcohol. 

Transfer  to  absolute  alcohol. 

Transfer  to  xylol. 

Transfer  to  fresh  xylol. 

Mount  in  xylol-balsam. 

If  an  alcohol  stain  is  used  instead  of  an  aqueous  one,  the  carrying 
down  and  up  through  the  graded  alcohols  is  omitted. 

If  it  is  desired  to  stain  double  with  eosin-hsematoxylin  (page  20) 
use  the  above  technic  in  staining  with  haematoxyhn;  then  the  alcoholic 
eosin  stain  before  final  transfer  to  absolute  alcohol. 


GENERAL  TECHNIC  25 


IX.  Injection 


For  the  study  of  the  distribution  of  the  blood-vessels  in  tissues 
and  organs,  it  is  often  necessary  to  make  use  of  sections  in  which 
the  blood-vessels  have  been  injected  with  some  transparent  coloring 
matter.  The  injecting  fluid  most  commonly  used  is  a  solution 
colored  gelatin. 

The  gelatin  solution  is  prepared  by  soaking  i  part  gelatin  in  from 
5  to  ID  parts  water — the  proportion  depending  upon  the  consistence 
desired — and  when  soft,  melting  on  a  water-bath. 

Various  dyes  are  used  for  coloring  the  gelatin,  the  most  common 
being  Prussian  blue  and  carmine. 

Prussian  blue  gelatin  is  prepared  by  adding  saturated  aque- 
ous solution  Prussian  blue  to  the  gelatin  solution,  the  proportions 
depending  upon  the  depth  of  color  desired.  Both  solutions  should  be 
at  a  temperature  of  60°  C.  After  thoroughly  mixing,  the  blue  gelatin 
is  filtered  through  cloth. 

Carmine  gelatin  is  prepared  by  first  dissolving  i  gm.  carmine 
in  30  c.c.  distilled  water.  To  this  is  added  ammonia  until  the  mixture 
becomes  a  dark  cherry  red.  A  lo-per-cent.  aqueous  solution  of  acetic 
acid  is  next  added,  drop  by  drop,  with  constant  stirring  until  the  mix- 
ture becomes  neutral.  The  carmine  and  gelatin  solutions  both  being 
at  about  60°  C,  are  now  mixed  in  the  desired  proportions.  If  the 
carmine  injection  mass  is  alkahne,  it  diffuses  through  the  walls  of  the 
vessels;  if  acid,  there  is  a  precipitation  of  the  carmine  which  may 
interfere  with  its  free  passage  through  the  capillaries.  If,  however, 
the  alkaline  carmine  and  gelatin  be  first  mixed,  and  the  lo-per-cent. 
acetic  acid  solution  be  then  added  as  directed  above,  the  precipitated 
granules  are  so  fine,  even  with  an  acid  reaction,  that  they  readily  pass 
through  the  capillaries .  The  precipitation  of  the  carmine  in  the  shape 
of  coarser  granules  is  of  advantage  when  it  is  desired  to  have  an  in- 
jection mass  which  will  fill  the  arteries  or  veins  only,  without  passing 
over  into  the  capillaries. 

The  injecting  apparatus  consists  of  a  vessel  which  contains  the 
injection  mass,  and  some  means  of  keeping  the  latter  under  a  con- 
stant but  easily  varied  pressure.  With  the  vessel  is  connected  a  tube 
ending  in  a  cannula,  through  which  the  injection  is  made. 

A  very  simple  apparatus  consists  of  a  shelf  which  can  be  raised 
and  lowered,  and  upon  which  the  vessel  stands.  The  tube  connecting 
with  the  cannula  may  be  attached  to  a  faucet  in  the  vessel  or  to 


26  HISTOLOGICAL  TECHNIC 

a  bent  glass  tube  which  passes  into  the  top  of  the  vessel  and  acts  on 
the  principle  of  a  siphon. 

In  a  somewhat  more  elaborate  apparatus  the  injection  mass  is 
placed  in  a  closed  vessel,  and  this  is  connected  with  a  second  vessel 
containing  air  compressed  by  means  of  an  air  pump. 

Accurate  regulation  of  the  pressure  may  be  obtained  by  connect- 
ing the  injection  vessel  with  a  manometer. 

If  the  injection  is  to  occupy  considerable  time,  a  hot-water  bath 
in  which  the  gelatin  may  be  kept  at  an  even  temperature  is  also 
necessary. 

Whole  animals  or  separate  organs  may  be  injected.  For  injecting 
a  whole  animal,  the  animal,  which  is  usually  a  small  one  such  as  a 
guinea-pig,  rat,  mouse,  or  frog,  is  chloroformed,  the  tip  of  the  heart 
is  cut  away  and  a  cannula  is  inserted  through  the  heart  into  the  aorta. 
This  is  first  connected  with  a  tube  leading  to  a  bottle  containing 
warm  normal  sahne  solution.  Pressure  is  obtained  in  the  same 
manner  as  above  described  for  the  injection  mass.  By  this  means 
the  entire  arterial  and  venous  systems  are  thoroughly  washed  out 
until  the  return  flow  from  the  vena  cava  is  perfectly  clear.  The 
cannula  is  next  connected  with  the  tube  from  the  vessel  containing 
the  injection  mass,  the  pressure  being  only  sufficient  to  keep  the 
liquid  flowing.  When  the  injection  mass  flows  easily  and  freely  from 
the  vena  cava,  the  vessel  is  tied  and  the  pressure  is  increased  slightly 
and  continued  until  the  color  of  the  injection  mass  shows  clearly 
in  the  superficial  capillaries.  The  aorta  is  now  tied  and  the  animal 
immersed  in  cold  water  to  solidify  the  gelatin.  After  the  gelatin 
becomes  hard,  the  desired  organs  are  removed  and  fixed  and  hardened 
in  the  usual  way.  Sections  of  injected  material  are  usually  cut  rather 
thick,  that  the  vessels  may  be  traced  the  greater  distance. 

Better  results  are  frequently  obtained  by  injecting  separate 
organs.  This  is  accomphshed  by  injecting  through  the  main  artery 
of  the  organ  (e.g.,  the  lungs  through  the  pulmonary,  the  kidney 
through  the  renal) .  The  injection  is  best  done  with  the  organ  in  situ, 
although  it  may  be  accomplished  after  the  organ  has  been  removed. 
The  method  is  the  same  as  given  above  for  injecting  an  animal  in  toto. 
The  so-called  double  injection  by  means  of  which  an  attempt  is 
made  to  fill  the  arteries  with  an  injection  mass  of  one  color  (red), 
while  the  veins  are  filled  with  an  injection  mass  of  another  color 
(blue),  often  gives  pretty,  but  usually  inaccurate  pictures,  it  being, 
as  a  rule,  impossible  to  confine  each  injection  mass  to  one  system. 


GENERAL  TECHNIC  27 

Double  injection  is  accomplished  by  first  washing  out  the  vessels 
with  normal  saHne  and  then  connecting  the  artery  with  the  red  gelatin, 
the  vein  with  the  blue  gelatin,  and  injecting  both  at  the  same  time, 
the  pressure  driving  the  saline  out  of  the  vessels  into  the  tissues. 
The  difficulty  is  that  either  the  arterial  injection  carries  over  into 
the  veins,  or  the  venous  injection  carries  over  into  the  arteries.  A 
somewhat  more  accurate  method  is  first  to  inject  the  veins  with  an 
injection  mass  in  which  the  coloring  matter  is  in  the  form  of  granules 
too  large  to  pass  through  the  capillaries,  and  then  to  inject  the  arter- 
ies and  capillaries  in  the  usual  manner.  This  method  is  especially 
useful  in  demonstrating  the  vessels  of  the  kidney,  Hver,  and  gastro- 
intestinal canal. 


CHAPTER  II 
SPECIAL  STAINING  METHODS 

Or  these  only  the  more  common  will  be  described. 

(i)  Silver-nitrate  Method  op  Staining  Intercellular  Sub- 
stance.— ^After  first  washing,  the  tissue,  e.g.,  omentum  or  cornea, 
is  placed  in  a  from  0.2-  to  i-per-cent.  solution  of  silver  nitrate,  or 
better,  protargol,  where  it  is  kept  in  the  dark  for  a  half-hour  or  more 
according  to  the  thickness  and  density  of  the  tissue.  The  specimen 
is  then  washed  in  water,  transferred  to  40-per-cent.  alcohol  and  placed 
in  the  direct  sunlight  until  it  assumes  a  hght  brown  color.  It  is  then 
placed  in  fresh  80-per-cent.  alcohol  for  preservation. 

(2)  Chlorid  of  gold  in  i-per-cent.  aqueous  solution  is  used  in 
the  same  manner  for  demonstrating  connective-tissue  cells  and  their 
finer  processes. 

(3)  Weigert's  Elastic-tissue  Stain. — This  is  prepared  as 
follows : 

Fuchsin,  2  gm. 

Resorcin,  4  gm. 

Water,  200  c.c. 

These  are  boiled  for  five  minutes,  during  which  25  c.c.  of  liquor  ferri 
sesquichlorati  are  stirred  in.  The  result  is  a  precipitate  which  should 
be  filtered  out  after  the  Hquid  has  become  cool.  After  drying,  200 
c.c.  of  95-per-cent.  alcohol  are  added  to  the  filtrate  and  boiled  until 
the  latter  dissolves.  Lastly,  4  c.c.  of  hydric  chlorid  are  added  to 
the  solution.  Sections  should  remain  in  the  stain  thirty  minutes, 
after  which  they  are  washed  in  alcohol  until  the  stain  ceases  to  be 
given  off. 

(4)  Verhoefe's  Differential  Elastic  Tissue  Stain. — 

Haematoxylin  crystals  (Grubler),  0.15  gm. 

Absolute  alcohol,  25.00  c.c. 

Dissolve  by  heating,  then  add  5-per-cent.  aqueous  solution 
ammonium  hydrate,  i  drop.  Allow  to  stand  5  minutes  or 
longer,  then  add  Lugol's  solution  (iodin  2  parts,  potassium, 
iodid  4  parts),  22 . 00  c.c. 

Filter,  let  stand  in  corked  bottle  24  hours. 

28 


SPECL-^L  STAINING  METHODS  29 

In  using  this  stain  add  to  each  cubic  centimeter  required  of  the 
above  solution  i  drop  of  a  y-per-cent.  solution  of  ferric  chlorid  in 
absolute  alcohol. 

Sections  are  carried  from  alcohol  into  the  staining  fluid  where  they 
remain  one  to  three  hours.  The  stain  should  be  kept  covered  to 
prevent  evaporation.  Sections  are  next  washed  in  water  one  or  two 
minutes  and  examined  under  the  microscope.  If  further  differentia- 
tion is  desirable,  place  a  few  seconds  in  i-per-cent.  aqueous  solution 
ferric  chlorid.  Wash  in  water.  Counterstain  in  0.2-per-cent. 
eosin,  dehydrate  in  alcohol,  clear  and  mount  in  balsam. 

Elastic  tissue  is  stained  black,  nuclei  take  haematoxylin,  while 
other  connective  tissues,  myelin  and  neuroglia  stain  with  eosin. 
Fixation  by  Zenker's  fluid  gives  perhaps  the  best  results  although 
the  stain  may  be  used  after  other  fixations.  Water  in  the  staining 
fluid  causes  precipitates.  It  is  therefore  important  to  see  that  all 
dishes  used  are  perfectly  dry  or  washed  with  alcohol  before  using. 
Too  much  ferric  chlorid  gives  precipitates  and  overstaining,  too 
Httle  results  in  failure  of  the  elastic  fibres  to  stain. 

(5)  GoLGi's  Chrome-silver  Method  for  Demonstrating  Se- 
cretory Tubules.- — ^Small  pieces  of  perfectly  fresh  tissue,  e.g.,  hver, 
are  placed  in  the  following: 

Potassium  bichromate,  4-per-cent.  aqueous  solution,    4  vols. 
Osmic  acid,  i-per-cent.  aqueous  solution,  i  vol. 

After  three  days  they  are  transferred  without  washing  to  a  0.75-per- 
cent, aqueous  solution  of  silver  nitrate,  which  should  be  changed  as 
soon  as  a  precipitate  forms.  The  specimens  remain  in  the  second 
silver  solution  from  two  to  three  days,  after  which  they  are  rapidly 
dehydrated,  embedded  in  celloidin,  and  cut  into  rather  thick  sections. 

(6)  Mallory's  Phosphomolybdic  Acid  H.<ematoxylin  Stain  for 
Connective  Tissue. — Thin  sections  are  placed  for  from  two  to  ten 
minutes  in  a  lo-per-cent.  aqueous  solution  of  phosphomolybdic  acid. 
They  are  then  washed  in  distilled  water  and  transferred  to : 

Phosphomolybdic  acid,  lo-pcr-cent.  aqueous  solution,  100. o  c.c. 
Distilled  water,  200.0  c.c. 

Haematoxylin  crystals,  1.75  gm. 

Carbolic-acid  crystals,  5  .  00  gm. 

The  phosphomolybdic  acid  and  water  are  first  mixed,  after  which 
the  ha.'matoxylin  and  carbolic  acid  are  added. 

After  staining  from  Icn  to  twenty  minutes  the  sections  are  washed 


30  HISTOLOGICAL  TECHNIC 

in  distilled  water,  placed  for  five  minutes  in  50-per-cent.  alcohol,  then 
in  strong  alcohol,  cleared  in  xylol  and  mounted  in  xylol-balsam. 
This  stain  works  best  after  Zenker's  fluid  fixation. 

(7)  Mallory's  Phosphotungstic  Acid  Hematoxylin  Stain  for 
Connective  Tissue. 

Haematoxylin  (or  hEematein  ammonium),  o.  i  gm. 

Water,  80.     c.c. 

Phosphotungstic  acid  (Merck),  lo-per-cent.  aqueous 

solution,  20.    c.c. 

The  hgematoxylin  should  be  dissolved  in  a  little  water  with 
the  aid  of  heat  and,  when  cool,  added  to  the  rest  of  the  solution. 
Allow  to  ripen  for  several  weeks  or  months.  Or,  if  it  is  de- 
sired for  immediate  use,  the  solution  can  be  ripened  by  the 
addition  of  10  c.c.  of  a  1/4-per-cent.  sohition  of  potassium  per- 
manganate. 

Tissues  should  be  fixed  in  Zenker's  fluid  (p.  8). 

1.  Treat  sections  with  iodin  solution  to  remove  mercury  precipi- 
tate, 5  to  10  minutes  (p.  9.) 

2.  Several  changes  95-per-cent.  alcohol. 

3.  Water. 

4.  One-fourth-per-cent.  aqueous  solution  potassium  permangan- 
ate, 5  to  10  minutes. 

5.  Wash  in  water. 

6.  Five-per-cent.  aqueous  solution  oxalic  acid,  5  to  10  minutes. 

7.  Wash  thoroughly  in  water. 

8.  Phosphotungstic  acid  haematoxylin  solution,  twelve  to  twenty- 
four  hours. 

9.  Dip  for  a  few  seconds  in  95-per-cent.  alcohol. 

10.  Clear  in  carbol-xylol  and  xylol  and  mount  in  xylol-damar. 
(8)  Mallory's  Aniline  Blue   Stain   for    Connective    Tis- 
sue.— Tissues  should  be  fixed  in  Zenker's  fluid  (p.  8). 

1.  Stain  thin  sections  in  a  0.2-per-cent.  aqueous  solution  of  acid 
fuchsin  for  five  to  ten  minutes.     (This  step  may  be  omitted.) 

2.  Stain  in  the  following  solution  for  twenty  minutes: 

Aniline  blue  (soluble  in  water),  0.5  gm. 
Orange  G.,  2.0  gm. 
Phosphomolybdic  acid,   i-per-cent.  aqueous  solu- 
tion, 100. o  c.c. 

3.  Decolorize  in  several  changes  of  95-per-cent.  alcohol. 

4.  Clear  in  carbol-xylol  and  xylol  and  mount  in  xylol-damar. 


speci.\l  staining  methods  31 

(9)  ^SIaresh's  Modification  of  Bielschowskys'  Stain  for 
THE  Finer  Connective  Tissue  Fibrils. 

1.  Very  thin  paraffin  sections  are  iixed  to  the  sHde  and  placed  for 
twelve  to  twenty-four  hours  in  a  2-per-cent.  silver  nitrate  solution. 

2 .  For  fifteen  to  thirty  minutes  in  freshly  prepared  alkaline  silver 
solution  (20  c.c.  of  2-per-cent.  silver  nitrate  solution,  to  which  have 
been  added  3  drops  of  40-per-cent.  caustic  soda,  and  the  precipitate 
redissolved  by  adding  ammonia  drop  by  drop  while  stirring). 

3.  Rinsed  quickly  in  distilled  water  and  placed  in  20-per-cent. 
formalin  for  three  minutes  or  until  black. 

4.  Washed  in  distilled  water  and  transferred  for  ten  minutes  to 
acid  gold  bath  (10  c.c.  distilled  water  to  which  have  been  added  2 
or  3  drops  of  i-per-cent.  gold  chlorid  and  2  or  3  drops  acid). 

5.  Placed  one-half  to  one  minute  in  5-per-cent.  hyposulphite  of 
soda  to  remove  all  unreduced  silver. 

6.  Washed  in  distilled  water,  dehydrated,  cleared  in  xylol  and 
mounted  in  balsam. 

(10)  OsMic-ACiD  Stain  for  Fat. — For  this  purpose  osmic  acid 
is  used  in  a  i-per-cent.  aqueous  solution.  The  method  is  especially 
useful  for  demonstrating  developing  fat,  fatty  secretions  (mammary 
gland),  and  fat  absorption  (small  intestine).  Very  small  bits  of  the 
tissue  are  placed  in  the  osmic-acid  solution  for  from  twelve  to  twenty- 
four  hours.  They  are  then  hardened  in  graded  alcohols,  embedded 
in  celloidin,  and  the  sections  mounted  in  glycerin. 

(11)  Jenner's  Blood  Stain. 

Water-soluble  eosin  (Griibler),  i-per-cent.  aqueous 

solution,  100  c.c. 

Methylene  blue — pure  (Griibler),  i-per-ccnt.  aqueous 

solution,  100  c.c. 

Mix,  and  after  standing  24  hours,  filter.     The  filtrate  is 

dried  at  65°  C,  washed,  again  dried  and  powdered. 

To  make  the  staining  solution,  0.5  gm.  of  the  powder  is  dissolved 
in  100  c.c.  pure  methyl  alcohol.  Blood  smears  stain  in  from  two  to 
five  minutes.  They  are  then  washed  in  water,  dried,  and  mounted 
in  balsam. 

This  solution  acts  as  a  fixative  as  well  as  a  stain. 


CHAPTER  III 
SPECIAL  NEUROLOGICAL  STAINING  METHODS 

Weigert's  Method  of  Staining  Medullated  Nerve  Fibres 

In  preparing  material  for  the  Weigert  method,  two  points  are  to 
be  kept  in  mind:  ist,  proper  fixation  and  preservation  of  the  myelin 
sheaths;  2d,  treatment  (mordanting)  with  a  reagent  which  enters 
into  combination  with  the  myeUn,  the  result  being  that  the  myelin 
sheaths  stain  specifically  with  hsematoxylin.  Formalin  fulfils  the 
first  requirement,  the  bichromates  the  first  and  second.  Consequently 
the  material  may  be  fixed  and  hardened  in  bichromate,  and,  if  not 
to  be  used  immediately,  is  best  kept  in  formalin  to  avoid  overharden- 
ing.  Or  the  material  may  be  fixed  and  kept  in  formalin  and  impreg- 
nated with  the  bichromate  before  using,  the  latter  being  done  before 
dehydrating  in  alcohol.  Further  mordanting,  which  is  usually  done, 
especially  when  the  material  has  been  kept  for  some  time  in  formalin 
or  alcohol,  is  for  the  purpose  of  intensifying  the  stain. 

Material  is  fixed  in  one  of  the  following  fluids: 

(a)  Miiller's  fluid  (page  7). 

(b)  Potassium  bichromate,  5-per-cent.  aqueous  solution. 

(c)  Formalin,  lo-per-cent.  aqueous  solution. 

(d)  FormaHn,  i  volume;  potassium  bichromate,  5-per-cent. 
aqueous  solution,  9  volumes. 

In  Miiller's  fluid  or  in  plain  potassium-bichromate  solution  a 
hardening  of  two  days  to  four  weeks  is  required;  in  formaHn  or 
formaHn-bichromate  from  a  week  to  ten  days  is  sufficient.  All 
material  is  better  kept  until  used  in  5-per-cent.  to  lo-per-cent. 
formaHn  solution  than  in  alcohol.  The  specimens  are  then  hardened 
in  graded  alcohols,  embedded  in  celloidin,  and  sections  cut  in  the 
usual  way.  Material  fixed  in  formalin  should  be  placed  for  several 
days  in  the  following: 

Chrome  alum,  i  gm. 

Potassium  bichromate,  3  gm. 

Water,  100  c.c. 

before  hardening  in  alcohol. 

32 


SPECIAL  NEUROLOGICAL  STAINING  METHODS  33 

Sections  from  material  fixed  in  any  of  the  chrome-salt  solutions 
are  placed  for  from  twelve  to  twenty-four  hours  in  a  saturated  aque- 
ous solution  of  neutral  cupric  acetate  diluted  with  an  equal  volume  of 
water.  The  cupric  acetate  forms  some  combination  with  the  tissues 
which  intensifies  their  staining  quaHties,  thus  acting  Hke  the  chrome 
salts  as  a  mordant. 

After  mordanting,  the  sections  are  washed  in  water  and  trans- 
ferred to  the  following  staining  fluid: 

Haematoxylin  crystals,  i  gm. 

Alcohol,  9S-per-cent.,  lo  c.c. 

Lithium  carbonate — saturated  aqueous  solution,  i  c.c. 

Water,  90  c.c. 

This  solution  must  either  be  freshly  made  before  using,  the  haema- 
toxylin being  dissolved  first  in  the  alcohol,  or  the  haematoxylin  may 
be  kept  in  lo-per-cent.  alcohoHc  solution,  the  lithium  carbonate  in 
saturated  aqueous  solution,  and  the  staining  fluid  made  from  these 
as  needed. 

Sections  remain  in  the  haematoxylin  solution  from  two  to  twenty- 
four  hours,  the  longer  time  being  required  for  staining  the  finer  fibres 
of  the  cerebral  and  cerebellar  cortices.  They  are  then  washed  in 
water  and  decolorized  in  the  following: 

Potassium  ferricyanid,  2 . 5  gm. 

Sodium  biborate,  2.0  gm. 

Water,  300.0  c.c. 

While  in  the  decolorizer,  sections  should  be  gently  shaken  or  moved 
about  with  a  glass  rod  to  insure  equal  decolorization.  In  the  decolor- 
izer the  sections  lose  the  uniform  black  which  they  had  on  removal 
from  the  haimatoxyhn.  They  remain  in  the  decolorizing  fluid  until 
the  gray  matter  becomes  a  Hght  gray  or  yellow  color,  in  sharp  con- 
trast with  the  white  matter  which  remains  dark.  Sections  are  then 
washed  in  several  waters  to  remove  all  traces  of  decolorizer,  and  de- 
hydrated in  alcohol. 

Weigert-Pal  Method. — In  this  modification  of  the  Weigert 
method,  material  hardened  in  formahn  should  be  further  hardened  in 
potassium  bichromate  5-per-cent.  for  two  weeks,  or  in  copper  bichro- 
mate 3-per-cent.  for  about  a  week,  after  which  it  may  be  cut  and 
stained  without  further  mordanting.  Sections  from  material  hard- 
ened in  the  other  above-mentioned  ways  are  mordanted  in  a  3-  to  5- 
per-cent.  aqueous  solution  of  potassium  bichromate  instead  of  in  the 


34  HISTOLOGICAL  TECHNIC 

copper-acetate  solution.  After  rinsing  in  water  the  sections  are 
stained  in  hgematoxylin  as  in  the  ordinary  Weigert  method.  The 
lithium  carbonate  may,  however,  be  omitted.  They  are  then  washed 
and  transferred  to  a  0.25-per-cent.  solution  of  potassium  permanga- 
nate, where  they  remain  from  one-half  to  two  minutes,  after  which 
they  are  again  washed  and  placed  in  the  following: 

Oxalic  acid,  i  gm. 

Potassium  sulphite,  i  gm. 

Water,  200  c.c. 

In  this  solution  differentiation  takes  place,  the  medullary  sheaths 
remaining  dark,  while  the  color  is  entirely  removed  from  the  rest  of 
the  tissue.  If  the  section  is  still  too  dark,  it  may  again  be  carried 
through  the  permanganate  and  oxaUc-acid  solutions,  rinsing  in  water 
between  changes,  until  sufficiently  decolorized. 

All  formahn-fixed  material  is  best  stained  by  the  Weigert-Pal 
method.  An  intensification  of  the  stain,  especially  of  the  very  fine 
fibres,  may  sometimes  be  obtained  by  placing  the  sections  for  a  min- 
ute in  a  0.5-per-cent.  aqueous  solution  of  osmic  acid  before 
decolorizing. 

Marchi's  Method  for"  Staining  Degenerating  Nerves 

Small  pieces  of  tissue  are  fixed  and  hardened  for  from  seven  to 
ten  days  in  Miiller's  fluid.  Thin  sHces  of  the  tissue  are  then  trans- 
ferred to  a  solution  of  one  part  i-per-cent.  osmic  acid  and  two  parts 
Miiller's  fluid,  in  which  they  remain  from  two  to  seven  days.  After 
embedding  and  sectioning  in  the  usual  manner,  sections  are  mounted, 
usually  without  further  staining,  in  xylol-balsam.  The  treatment 
with  Miiller's  fluid  so  affects  the  normal  medullary  sheaths  that  they 
will  not  take  the  osmic-acid  stain,  but  appear  yellowish-brown,  while 
the  degenerating  sheaths  (probably  fatty)  stain  black.  The  result 
is  a  positive  picture  of  stained  degenerating  fibres  in  contrast  with  the 
stained  normal  and  unstained  degenerated  fibres  as  seen  after  Weigert 
staining.  Another  advantage  of  the  Marchi  method  is  that,  as  the 
picture  is  a  positive  one,  an  early  or  sHght  degeneration  may  be  recog- 
nized which  would  escape  notice  in  material  stained  by  Weigert' s 
method;  on  the  other  hand,  in  a  long-standing  degeneration  when  the 
medullary  sheaths  have  completely  disappeared  and  their  places  have 
been  taken  by  connective  tissue,  there  being  no  degenerated  myelin 
remaining,  the  Marchi  method  is  inappHcable. 


SPECL\L  XEUROLOGIC.\L  STAINING  METHODS  35 

Busch's  modification  of  the  Marchi  method  gives  sharp  pictures 
and  has  the  advantage  of  allowing  formaldehyd  fijcation  and  harden- 
ing. Tissues  thus  treated  are  placed  for  from  five  to  seven  days  in  a 
solution  of  one  part  osmic  acid,  three  parts  iodate  of  sodium,  and  300 
parts  water.     They  are  then  embedded,  cut,  and  mounted  as  usual. 

GoLGi  Methods  of  Staining  Nerve  Tissue 

The  Golgi  methods  in  most  common  use  at  present  are  the  fol- 
lowing : 

(i)  Golgi  Silver  Methods.- — (a)  Slow  Method. — Blocks  of  tis- 
sue are  placed  for  several  months  in  a  3-per-cent.  aqueous  solution  of 
potassium  bichromate.  Small  pieces  of  the  tissue  are  then  trans- 
ferred immediately  to  a  0.75-per-cent.  aqueous  solution  of  silver 
nitrate.  This  is  changed  several  times  or  until  no  more  precipitate 
is  formed.  In  the  last  silver  solution  they  remain  for  from  one  to 
three  days.  The  only  method  of  determining  whether  the  tissue  has 
been  sufficiently  long  in  the  bichromate  is  to  try  at  intervals  small 
bits  of  the  tissue  in  the  silver  solution  until  a  satisfactory  result  is 
secured.  Sections  should  usually  be  from  50  to  80  p.  thick  and  are 
mounted  in  balsam  without  a  cover-glass. 

(b)  Rapid  Method. — Small  pieces  of  tissue,  2  to  4  mm.  thick,  are 
placed  in  the  following  solution  for  from  two  to  six  days,  the  time 
depending  upon  the  age  and  character  of  the  tissue,  the  temperature 
at  which  fixation  is  carried  on,  and  the  elements  which  it  is  desired 
to  impregnate: 

Osmic  acid,  i-per-cent.  aqueous  solution,  i  part. 

Potassium  bichromate,  3 .  5-per-cent.  aqueous  solution,  4  parts. 

As  a  rule,  the  longer  the  hardening  the  fewer  are  the  elements  stained, 
but  these  few  are  clearer.  The  tissue  is  next  transferred  to  silver 
nitrate  as  in  the  slow  method.  Pieces  of  tissue  should  be  tried  each 
day  until  a  satisfactory  result  is  obtained.  The  pieces  may  be  kept 
in  silver  nitrate  some  time,  but  not  in  alcohol,  and  are  better  cut  with- 
out embedding,  the  pieces  being  simply  washed  in  95-per-cent. 
alcohol  several  hours,  then  gummed  to  the  block  with  celloidin,  cut  in 
95-pcr-cent.  alcohol,  and  mounted  as  in  the  slow  method. 

(c)  Mixed  Method. — Specimens  are  placed  in  the  bichromate 
solution  for  about  four  days,  then  from  one  to  three  days  in  the 
osmium-bichromate  mixture  (see  Rapid  Method),  after  which  they 
are  transferred  to  the  silver  solution  (see  Slow  Method). 


36  HISTOLOGICAL  TECHNIC 

{d)  Formalin-bichromate  Method. — Tissues  are  placed  for  from  two 
to  six  days  in  the  following  solution: 

Formalin,  lo  to  20  parts. 

Potassium  bichromate,  3-per-cent.  aqueous 

solution,  90  to  80  parts. 

Subsequent  treatment  with  silver  is  the  same  as  in  the  previously 
described  method.  The  results  resemble  those  of  the  slow  method. 
The  specimens  may  be  kept  in  strong  alcohol.  The  method  is  satis- 
factory only  for  the  adult  cerebrum  and  cerebellum. 

(2)  GoLGi  BiCHLORiD  METHOD. — Material,  which  need  not  be 
cut  into  small  pieces,  remains  for  several  months  in  the  potassium- 
bichromate  solution  (see  Slow  Silver  Method),  after  which  it  is 
transferred  to  a  0.25-per-cent.  to  i-per-cent.  aqueous  solution  of 
mercuric  chlorid  for  from  four  to  twelve  months  or  longer,  the 
solution  being  changed  as  often  as  discolored.  The  degree  of  impreg- 
nation must  be  determined  by  frequently  testing  the  material,  but  is 
usually  indicated  by  the  appearance  of  small  white  spots  on  the  sur- 
face of  the  tissue. 

A  modification  of  the  bichlorid  method,  known  as  the  Cox-Golgi 
Method,  often  gives  good  results.  The  following  fixing  solution  is 
used: 

Potassium  bichromate,  5-per-cent.  aqueous  solution,        20  parts. 
Mercuric  chlorid,  5-per-cent.  aqueous  solution,  20  parts. 

Distilled  water,  40  parts. 

After  mixing  the  above,  add 

Potassium  chromate,  5-per-cent.  aqueous  solution,  16  parts. 

Tissues  remain  in  this  fluid  for  from  two  to  five  months. 

In  the  Golgi  silver  methods  the  result  of  the  treatment,  first  with 
bichromate  and  then  with  silver  nitrate,  is  that  a  precipitate  is  formed 
in  the  tissue,  a  chromate  or  some  other  silver  salt,  which  in  favorable 
cases  is  largely  confined  to  certain  of  the  nerve  cells  and  their  proc- 
esses. It  must  be  remembered  that  only  a  few  of  the  cells  and  proc- 
esses are  stained,  these  often  only  partially,  and  that  other  irregular 
precipitations  are  usually  present.  In  the  mercury  methods,  the 
bichromate  of  potassium  and  the  bichlorid  of  mercury  may  be  used 
combined  in  the  same  solution.  There  are  other  modifications  of 
the  Golgi  methods,  in  which  similar  precipitates  of  other  metalHc 
salts  are  secured. 


SPECL\L  NEUROLOGICAL  STAINING  METHODS  37 

Golgi  specimens  should  be  dehydrated  and  embedded  as  rapidly 
as  possible.  This  is  especially  true  of  specimens  treated  by  the  rapid 
and  the  mixed  methods.  Those  treated  by  the  slow  silver  method 
and  by  the  bichlorid  method  are  more  permanent,  and  more  time  may 
be  taken  with  their  dehydration.  Thick  sections  should  be  cut  (75 
to  100//)  and  mounted  in  xylol-balsam.  After  the  rapid  method,  it  is 
safer  to  mount  without  a  cover-glass;  after  the  slow  method,  speci- 
mens may  be  mounted  with  or  without  a  cover.  The  balsam  should 
be  hard,  and  melted  at  the  time  of  using.     (See  Mounting,  page  22.) 

Cajal's  Methods  for  Staining  the  Neurofibrils  in  the 

Nerve-cells 

In  these  methods,  besides  the  neurofibrils,  the  cell  processes  and 
especially  the  axis  cyHnders  are  often  beautifully  displayed,  the  stain 
giving  a  picture  in  this  respect  much  more  general  than  that  of  the 
Golgi  methods,  but  much  more  specific,  and  sharper  than  that  of  the 
ordinary  stains. 

The  methods  consist  mainly  of  two  steps:  (i)  The  staining  of  the 
tissue  in  a  solution  of  silver  nitrate;  (2)  the  further  reduction  of  the 
silver  stain  with  a  weak  photographic  developer.  Three  methods, 
or  variations,  are  here  given: 

(i)  Pieces  about  0.5  cm.  thick  are  placed  in  a  liberal  quantity  of 
from  i-per-cent.  or  1.5-per-cent.  (new-born  or  embryonic  mammalian 
material)  to  5-per-cent.  (adult  material)  solution  of  silver  nitrate  and 
kept  at  a  temperature  of  32°  to  40°  C.  for  two  to  five  days.  When 
properly  stained  (shown  by  a  yellowish  or  light  brown  coloration  of 
freshly  cut  surfaces)  the  pieces  are  very  briefly  rinsed  in  distilled 
water  and  placed  in:  pyrogallol  (or  hydroquinone)  i  gm.,  distilled 
water  100  c.c,  formahn  5  to  10  c.c,  for  twenty-four  hours  or  more. 
They  are  then  washed  a  few  minutes  in  water  and  transferred  to 
95-per-cent.  alcohol,  which  is  changed  when  discolored,  and  where 
they  may  often  be  kept  for  some  time  without  injury.  They  may 
then  be  embedded  in  celloidin  or  paraffin  and  sections  cut,  usually 
15-25/J'.  in  thickness.  Different  depths  of  the  blocks  of  tissue  usually 
vary  in  stain,  the  most  favorable  being  intermediate  between  the 
surface  and  centre  of  the  block.  Celloidin  sections  usually  keep  well 
in  95-per-cent.  alcohol.  They  may  be  cleared  in  carbol-xylol, 
rinsed  in  xylol,  and  mounted  in  xylol-balsam  or  xylol-damar  in 
the  usual  way.     In  delicate  objects  (study  of  j)athological  changes 


38  HISTOLOGICAL  TECHNIC 

in  neurofibrils)  it  may  be  best  to  abbreviate  the  dehydration,  and 
block  and  cut  without  infiltration  with  celloidin. 

(2)  Pieces  are  first  placed  in  95-per-cent.  alcohol  or  in  absolute 
alcohol  (32°  to  40°  C.)  for  twenty-four  hours.  For  neurofibrils  it  is 
better  to  add  from  0.25  c.c.  to  i  c.c.  of  ammonium  hydrate  to  each 
10  c.c.  of  the  alcohol.  They  are  then  treated  with  silver  nitrate  i-per- 
cent.  or  1.5-per-cent.,  as  in  (i).  This  method  gives  better  pictures 
of  the  cell  processes  and  axis  cylinders  and  a  better  fixation  of  the 
cells. 

(3)  Pieces  are  first  placed  in  distilled  water  100  c.c,  formalin 
20  c.c,  ammonia  i  c.c,  for  twenty-four  hours  at  32°-4o°  C,  washed 
in  water  twelve  to  twenty-four  hours,  and  then  treated  with  silver 
nitrate  i-per-cent.  or  1.5-per-cent.,  as  in  (i).  This  method  gives 
pictures  of  the  terminations  of  nerve  fibres  on  the  periphery  of  nerve 
cells  and  their  dendrites  (end-feet  or  end-buttons  of  Aaerbach). 

In  general  it  is  best  to  avoid,  in  the  above  methods,  any  excessive 
exposure  to  the  light  while  the  pieces  are  in  the  silver  bath  (especially 
when  the  pieces  are  very  small),  though  they  may  be  brought  into 
the  light  for  examination  and  while  being  transferred  to  the  reducing 
fluid. 

Nissl's  Method 

This  method  is  useful  for  studying  the  internal  structure  of  the 
nerve  cell.  It  depends  upon  a  rapid  fixation  of  the  tissue,  its  sub- 
sequent staining  with  an  aniline  dye,  and  final  decolorization  in 
alcohol. 

The  aniline  dye  most  commonly  used  is  methylene  blue.  There 
are  many  variations  and  modifications  of  Nissl's  method.  The 
following  is  simple  and  gives  uniformly  good  results : 

Specimens  are  first  fixed  in  mercuric-chlorid  solution  (page  8), 
in  formalin  (lo-per-cent.  aqueous  solution),  or  in  absolute  alcohol, 
and  embedded  in  celloidin. 

Thin  sections  are  stained  in  a  i-per-cent.  aqueous  solution  of 
pure  methylene  blue  (Griibler).  The  sections  are  gently  warmed  in 
the  solution  until  steam  begins  to  be  given  off.  They  are  then 
washed  in  water  and  differentiated  in  strong  alcohol.  The  degree  of 
decolorization  which  gives  the  best  results  can  be  learned  only  by 
practice.  Several  alcohols  must  be  used,  and  the  last  alcohol  must 
be  perfectly  free  from  methylene  blue.     The  sections  are  cleared  in 


SPECL\L  XEUROLOGIC.\L  STAINING  METHODS  39 

equal  parts  xylol  and  cajeput  oil  and  mounted  in  xylol-balsam.  A 
contrast  stain  may  be  obtained  by  having  a  little  eosin  or  erythrosin 
in  the  last  alcohol. 

General  References  for  Further  Study  of  Technic. 

Freeborn:  Histological  Technic.     Reference  Handbook  of  Medical  Sciences, 
vol.  iv. 

Lee:  The  Microtomist's  Vade-mecum. 
^MaUory  and  Wright:  Pathological  Technic. 


PART  11 
THE  CELL 


CHAPTER  I 

THE  CELL 

In  the  simplest  forms  of  animal  life  the  entire  body  consists  of  a 
little  albuminous  structure,  the  essential  peculiarity  of  which  is  that 
it  possesses  properties  which  we  recognize  as  characteristic  of  living 
organisms.  This  albuminous  material  basis  of  life  is  known  as  pro- 
toplasm, while  the  structure  itself  is  known  as  a  cell.  Within  the 
cell  is  usually  found  a  specially  formed  part,  the  nucleus.  Peripher- 
ally cells  are  Hmited  by  a  modified  surface  cytoplasm  or  a  more  or 
less  distinct  cell  wall  or  cell  membrane. 


Fig.  I. — Diagram  of  a  tjqiical  cell,  i,  Cell  membrane.  2,  Metaplasm  granules. 
3,  Karyosome  or  net-knob.  4,  Hyaloplasm.  5,  Spongioplasm.  6,  Linin  network. 
7,  Nucleoplasm.  8,  .Vttraction-sphere.  9,  Centrosome.  10,  Plastids.  11,  Chro- 
matin network.     12,  Nuclear  membrane.     13,  Nucleolus.     14,  Vacuole. 

An  actively  multiplying  cell  contains  a  minute  structure  associated 
with  the  reproductive  function  and  known  as  the  centrosome. 

A  typical  cell  thus  consists  of  the  following  structures  (Fig.  i): 
(i)  The  cell  body;  (2)  the  cell  membrane;  (3)  the  nucleus;  (4)  the 
centrosome.  Of  these  only  the  cell  body  with  its  modified  surface 
cytoplasm  or  cell  membrane  is  present  in  all  cells.  A  few  cells  con- 
tain, in  their  fully  developed  condition,  no  nuclei.  In  many  mature 
cells  it  is  impossible  to  distinguish  a  centrosome. 

All  plants  and  animals  consist  of  cells  and  their  derivatives,  and 
if  an  attempt  be  made  to  resolve  any  of  the  more  complex  living  struc- 

43 


44 


THE  CELL 


tures  into  its  component  elements,  it  is  found  that  the  smallest 
possible  subdivision  still  compatible  with  life  is  the  cell.  The  cell 
may  therefore  be  considered  as  the  histological  element  or  unit  of 

structure. 

I.  The  Cell  Body.— This  consists  of  a  viscid,  colorless,  semi-fluid 
substance,  belonging  to  the  general  class  of  albumens.  It  is  of  com- 
plex chemical  composition  containing  the  elements  carbon,  hydrogen, 
oxygen  and  nitrogen  in  quite  constant  proportions,   and  smaller 

variable  quantities  of  phos- 
phorus, sulphur,  iron  and 
other  substances.  It  con- 
tains a  pecuHar  nitrogenous 
proteid,  plastin.  Structurally 
it  can  be  differentiated  into 
a  formed  element,  spongio- 
plasm,  and  a  homogeneous 
element,  hyaloplasm.  Dis- 
tributed along  the  spongio- 
plastic  network  are  minute 
granules,  microsomes.  The 
exact  relations  which  these 
elements  bear  to  one  another 
and  to  the  cell  as  a  whole 
have  been  the  subject  of 
much  investigation  and  spec- 
ulation. The  earher  cytolo- 
gists  concerned  themselves  with  the  question  as  to  whether  proto- 
plasm was  homogeneous  {i.e.,  a  mere  solution  or  at  most  a  mixture 
of  various  substances)  or  had  a  definite  structure.  The  theory  of 
a  structureless  protoplasm  having  been  long  since  abandoned, 
the  question  as  to  the  character  of  the  protoplasmic  structure  still 
remains  unanswered. 

Altmann's  granule  theory  considers  protoplsm  as  composed  of  fine  granules 
embedded  in  a  gelatinous  intergranular  substance.  Altmann  believed  these 
granules  the  ultimate  vital  elements,  and  for  this  reason  gave  them  the  name  of 
bioblasts  (Fig.  2,h). 

According  to  Biitschli,  protoplasm  is  a  foam  or  emulsion,  the  microscopic 
appearance  of  which  can  be  simulated  by  artificial  emulsions.  He  ascribes  the 
appearance  of  a  reticulum  to  the  fact  that  each  little  foam  space  forms  a  complete 
cavity  filled  with  fluid,  the  cut  walls  of  these  spaces  giving  a  reticular  appearance 
on  section  (Fig.  2,  c  and  Fig.  3). 


Fig.  2. — Diagram  Illustrating  Theories  of 
Protoplasmic  Structure,  a,  Fibrillar  theory; 
b,  granule  theory;  c,  "foam"  theory.  (The 
general  structure  of  cell  body  and  nucleus  cor- 
responds.) 


THE  CELL 


45 


Other  investigators  consider  protoplasm  as  made  up  of  (i)  a  fibrillar  element, 
either  in  the  form  of  a  network  of  anastomosing  fibrils  (cytoreticulum)  or  of  a 
feltwork  of  independent  fibrils  (filar  mass  or  miton),  and  (2)  a  fluid  or  semi-fluid 
substance   which   fills   in   the  meshes  of  the 
reticulum   or   separates   the  fibrils  (interfilar 
mass  or  paramiton)  (Fig.  2,  a). 

That  the  question  as  to  the  ultimate  struc- 
ture of  protoplasm  still  remains  unanswered  is 
dependent  mainly  upon  the  extreme  technical 
difl&culties  which  have  confronted  the  cytolo- 
gist.  Liv-ing  protoplasm  has  a  homogeneous 
glossy  appearance,  showing  even  under  the 
highest  magnification  rarely  more  than  a 
granular  structure.  It  is  usually  only  after 
death  of  the  cell  and  the  use  of  chemical 
fixatives  and  stains,  that  the  so-called  "struc- 
ture" of  protoplasm  becomes  visib'e.  How 
closely  the  picture  presented  by  such  chem- 
ically treated  protoplasm  corresponds  to  the 
structure  of  living  protoplasm  is  as  yet  un- 
determined. It  is  quite  possible  that  the 
structure  even  of  undift'erentiated  protoplasm 
or  protoplasm  proper,  such  as  is  found  in 
early  embryonal  cells,  is  not  entirely  uniform. 
The  protoplasm  of  the  more  highly  specialized 
cells  certainly  differs  markedly  in  structure 
and  somewhat  in  chemical  composition  in 
different  cells.  It  even  differs  in  the  same 
cell  under  different  functional  conditions. 
These  differences  are  apparently  due  to  special 
development  of  the  protoplasm  for  its  peculiar 
functions.  Thus,  for  example,  in  the  muscle 
cell  and  the  nerve  cell  most  of  what  in  the  em- 
bryonal cell  was  undifferentiated  protoplasm 
has  become  differentiated  into  contractile  or 
conductile  fibers.  The  nucleus  and  a  small 
amount  of  undift'crentiated  or  less  differenti- 
ated protoplasm  remain  and  are  probably 
largely  active  in  maintaining  the  nutrition  of 
the  cell.  Such  changes  in  the  protoplasm  are 
of  course  permanent.  Temporary  or  periodic 
changes  in  the  structure  of  protoplasm  are  seen 
in  such  cells  as  the  secreting  cells  of  the  pan- 
creas or  of  the  salivary  glands  where  marked 

differences  in  the  protoplasm  occur,  dependent  upon  whether  the  cell  is  in  a 
resting,  or  actively  secreting  condition. 

Protoplasm  is  thus  probably  best  considered  as  the  material  basis 


Fig.  3. — Foam  or  emulsion  struc- 
ture of  protoplasm  according  to 
Batschli  (Hutschli).  A,  Epidermal 
cell  of  the  earthworm.  B,  Peri- 
pheral cytoplasm  of  sea  urchin's 
egg.  C,  .A.rtificial  emulsion  of  olive 
oil,  sodium  chlorid  and  water. 


46  THE  CELL 

of  cell  activity,  i.e.,  of  Kfe,  rather  than  as  a  substance  having  fixed 
and  definite  chemical  or  morphological  characteristics. 

It  is  convenient  to  use  the  term  protoplasm  to  mean  the  entire 
substance  of  the  cell,  karyoplasm  to  designate  the  protoplasm  of 
the  nucleus,  and  cytoplasm  the  protoplasm  of  the  cell  body  exclusive 
of  the  nucleus. 

Peculiar  bodies  known  as  plastids  (Fig.  i)  are  of  frequent  occur- 
rence in  vegetable  cells,  and  are  also  found  in  some  animal  cells. 
They  are  apparently  to  be  regarded  as  a  differentiation  of  the  cyto- 
plasm, but  possess  a  remarkable  degree  of  independence,  being 
capable  of  subdivision  and  in  some  cases  of  existence  outside  of 
the  cell. 

In  addition  to  the  granules  which  are  apparently  an  integral  part 
of  the  protoplasmic  structure,  other  granules  and  various  cell  "inclu- 
sions" occur,  to  which  the  term  metaplasm  {paraplasm,  deutoplasm) 
granules,  has  been  appHed  (Fig.  i).  Some  of  these  are  intimately 
associated  with  the  cell  activities  and  represent  either  food  substances 
in  process  of  being  built  up  into  the  protoplasm  of  the  cell  or  waste 
products   of   cell  metabolism.     Others,  such   e.g.,  as  the  glycogen 

granules  of  the  Hver  cell  or  the  mucous 
granules  of  the  mucous  cell,  are  specific 
secretion  products.  Still  others  are  fat 
droplets,  pigment  granules,  and  various 
excrementitious  substances. 

When  the  protoplasm  of  a  cell  can  be 
differentiated  into  a  central  granular  area 
and  a  peripheral  clear  area,  the  former  is 
known  as  endoplasm,  the  latter  as  exoplasm. 
Fig.  4.— Intracellular  canals     When  the  exoplasm  forms  a  distinct  Hmit- 

(tropnospongium)  of  a  ganglion      .  ^ 

cell  (E.  Holmgren).  ing  layer,  but  blends  imperceptibly  with 

the  rest  of  the  protoplasm,  it  is  known  as 
the  crusta. 

In  some  cells  minute  channels  or  canals  are  present  in  the  cyto- 
plasm (Fig.  4).  These  channels  may  contain  branching  processes 
from  other  cells,  forming  what  is  known  as  a  trophospongium.  Some 
intracellular  canals  are  apparently  secretory  in  character  and  may 
communicate  with  fine  intercellular  secretory  channels.  In  this  way 
the  secretion  of  such  cells  as  the  serous  cells  forming  the  demilunes 
of  mucous  tubules  (p.  222),  or  of  the  parietal  cells  of  the  stomach 
glands  (Fig.  155),  is  carried  to  the  lumen. 


THE  CELL  47 

2.  The  Cell  Membrane  (Fig.  i). — In  most  vegetable  cells  the  cell 
membrane  is  the  most  conspicuous  part  of  the  cell  and  was  responsible 
for  the  name  "cell"  which  the  seventeenth-century  botanists,  over- 
looking the  importance  of  the  enclosed  protoplasm,  gave  to  the  little 
spaces  or  caN-ities  of  which  they  thought  plants  composed.  A  distinct 
cell  membrane  is  present  in  but  few  animal  cells.  An  exception  is 
seen  in  the  fat  cell  where  a  distinct  membrane  exists.  In  most 
animal  cells  no  membrane  has  as  yet  been  demonstrated  and  this  has 
led  to  a  persistent  denial  of  the  existence  of  such  a  membrane.  It 
is  nevertheless  probable  that  most  if  not  all  animal  cells  have  some 
modification,  however  slight,  of  the  periphery  of  their  protoplasm 
which  serves  to  retain  the  protoplasm  within  definite  bounds,  to  pro- 
tect it  as  it  were  and  at  the  same  time  permit  osmosis.  When  a 
membrane  surrounds  the  cell,  it  is  known  as  the  pellicula;  when  cells 
He  upon  the  surface,  and  only  the  free  surface  of  the  cells  is  covered  by 
a  membrane,  it  is  known  as  the  cuticula. 

3.  The  Nucleus  (Fig.  i). — This  is  a  vesicular  body  embedded  in 
the  cytoplasm.  The  typical  nucleus,  like  the  typical  cell,  is  sphe- 
roidal, but  the  shape  of  the  nucleus  varies  for  different  cells  and  corre- 
sponds somewhat  to  the  shape  of  the  cell  body,  e.g.,  the  rod-shaped 
nucleus  of  the  elongated  smooth  muscle  cell.  It  may  also  be  modified 
by  intracellular  pressure  as,  e.g.,  in  the  mucous  cell  and  in  the  fat 
cell. 

The  position  of  the  nucleus  is  usually  near  the  center  of  the  cell. 
It  may,  however,  be  eccentric.  Such  eccentricity  may  be  due  to 
pressure  of  cell  contents  as,  e.g.,  in  the  mucous  cell  and  in  the  fat  cell. 
Considered  by  earher  cytologists  an  unessential  part  of  the  cell,  the 
nucleus  is  now  known  to  be  most  intimately  associated  with  cellular 
activities.  It  is  not  only  essential  to  the  carrying  on  of  the  ordinary 
metaboHc  processes  of  the  cell,  but  is  an  active  agent  in  the  phenomena 
of  mitosis,  which  in  most  cases  determine  cell  reproduction. 

As  a  rule,  each  cell  contains  a  single  nucleus.  Some  cells  contain 
two  nuclei  (quite  common  in  the  Uver  cell,  rare  in  the  ovum  and  in  the 
nerve  cell).  A  few  cells  contain  many  nuclei,  e.g.,  the  multinuclear 
"giant"  cells  of  the  spleen,  bone-marrow,  and  certain  tumors.  Some 
cells,  such  as  the  human  red  blood  cell  and  the  respiratory  epithehum, 
are,  in  their  mature  condition,  non-nucleated.  All  non-nucleated 
cells,  however,  contained  nuclei  in  the  earlier  stages  of  their  develop- 
ment. Non-nucleated  cells,  while  capable  of  performing  certain 
functions,  are  wholly  incapable  of  proliferation.     The  non-nucleated 


48  THE  CELL 

condition  must,  therefore,  be  regarded  as  not  only  a  condition  of  matur- 
ity, but  of  actual  senility,  at  least  so  far  as  reproductive  powers  are 
concerned. 

In  some  of  the  lowest  forms  of  animal  life,  the  nuclear  material 
instead  of  being  grouped  to  form  a  definite  body  or  nucleus,  is  more 
or  less  evenly  distributed  as  granules  through  the  cytoplasm. 

Chemically  the  nucleus  is  extremely  complex,  being  composed  of 
the  proteids  nuclein,  paranuclein,  Hnin,  paralinin,  and  amphipyrenin. 

Morphologically  also  the  nucleus  is  complex,  much  of  the  apparent 
structural  differentiation  being  determined  by  the  staining  reactions 
of  the  different  elements  when  treated  with  certain  aniline  dyes.  The 
nuclear  structures  and  their  relations  to  the  chemical  constituents  of 
the  nucleus  are  as  follows: 

(a)  The  nuclear  membrane  {amphipyrenin).  This  forms  a  limit- 
ing membrane  separating  the  nucleus  from  the  cell  protoplasm.  It 
is  doubtful  whether  the  nuclear  membrane  is  different  either  chemic- 
ally or  morphologically  from  the  nucleoreticulum.  It  is  wanting  in 
some  nuclei.  When  present  it  appears  from  its  staining  reactions  to 
be  structurally  continuous  with,  and  chemically  identical  with,  in  some 
cases,  the  linin,  in  others,  the  chromatin  of  the  intranuclear  network. 
It  may  be  complete,  or  fenestrated  allowing  free  communication  be- 
tween the  cytoplasm  and  the  nuclear  contents. 

(&)  The  intranuclear  network,  or  nucleoreticulum,  consists  of  a 
chromatic  element  {nuclein  or  chromatin)  and  of  an  achromatic  element 
(linin) .  The  linin  constitutes  the  groundwork  of  the  reticulum  along 
which  the  chromatin  granules  are  distributed.  At  nodal  points 
of  the  network  there  are  often  considerable  accumulations  of  chroma- 
tin. These  nodal  points,  at  first  thought  to  be  nucleoH,  are  now 
known  as  false  nucleoli,  or  karyosomes.  Instead  of  a  distinct  network 
there  may  be  disconnected  threads  or  simply  granules  of  chromatin. 
Chromatin  is  the  most  characteristic  of  the  chemical  constituents 
of  the  nucleus,  the  only  one  which  contains  phosphoric  acid,  and  also, 
apparently,  the  only  nuclear  substance  which  is  always  transmitted 
from  parent  to  daughter  cell  in  cell-division.  Fine  granules  have  been 
described  as  occurring  in  the  linin,  differentiated  from  chromatin  by 
the  fact  that  they  are  most  susceptible  to  acid  dyes,  while  chromatin 
takes  basic  dyes. 

(c)  The  nucleolus  or  plasmosome  {paranuclein,  pyrenin)  is  a  small 
spherical  body  within  the  nucleus.  Not  infrequently  there  are  sev- 
eral nucleoli.     Similar  cells  vary  as  to  the  number  of  nucleoli  they 


THE  CELL  49 

contain.  The  same  cell  may  vary  as  to  the  number  of  its  nucleoli 
under  varying  functional  conditions.  The  nucleolus  regularly  dis- 
appears during  mitosis,  and  during  functional  acti\Tity  in  some 
gland  cells.  It  stains  intensely  with  basic  dyes.  Its  function  is 
unknown. 

(d)  Karyoplasm  {nucleoplasm,  nuclear  fluid,  nuclear  sap).  This  is 
the  fluid  or  semi-fluid  material  which  fills  in  the  meshes  of  the  nucleo- 
reticulum. 

While  the  nucleus  is  a  perfectly  distinct  structure  capable  in 
some*  animal  and  in  some  vegetable  cells  of  moving  about  more  or 
less  actively  in  the  cytoplasm,  and  is  usually  separated  by  a  membrane 
from  the  rest  of  the  cell,  a  marked  similarity  exists  between  the 
structure  of  nucleoplasm  and  cytoplasm. 
This  similarity  is  emphasized  by  the  absence 
in  some  resting  cells  of  any  nuclear  mem- 
brane, by  the  apparent  direct  continuity  in 
some  cases  of  nucleoreticulum  and  cytoretic- 
ulum,  and  by  the  continuity  of  karyoplasm 
and  cytoplasm  in  all  cells  during  cell-division. 

4.  The   centrosome    (Fig.    5)  is  a  small 

spheroidal    body    found    sometimes   in    the         -pio.     5. Spermatogo- 

nucleus,  or  more  commonly  in  the  cytoplasm     niumfrom  frog  (Hermann). 

Single  centrosome  at  cen- 

near  the  nucleus.  In  actively  dividmg  cells  ter  of  attraction  sphere  or 
the  centrosome  is  frequently  double,  this  ^^^^^fZ^""'  '^''''^^'  ^ 
being  apparently  in  preparation  for  the  suc- 
ceeding cell-division.  In  some  cases  the  centrosome  is  triple  or  even 
multiple.  It  was  first  found  in  the  ovum  and  described  as  peculiar  to 
that  cell.  It  is  now  beHeved  to  occur  in  most,  if  not  in  all,  animal 
cells.  It  usually  consists  of  (i)  a  minute  central  granule  or  granules— 
the  centriole,  which  stains  intensely  with  iron-haematoxylin,  and  out- 
side of  which  is  (2)  a  clear  zone,  the  attraction  sphere.  From  this 
centre,  radiations  extend  outward  into  the  cytoplasm.  There  is  much 
confusion  of  terms  in  connection  with  the  centrosome,  the  term  cen- 
trosome being  by  some  applied  to  the  entire  structure  including  the 
radiating  fibrils,  by  others  to  the  central  granule  only,  by  still  others 
to  the  central  granule  plus  the  surrounding  clear  area.  By  some  the 
radiations  are  believed  to  be  composed  of  a  different  substance  than 
the  general  cytoplasm,  which  is  designated  archoplasm.  The  main 
significance  of  the  centrosome  is  in  connection  with  cell-division, 
under  which  head  it  will  be  further  considered  (p,  53). 


50  THE  CELL 

Vital  Properties  of  Cells 

It  has  already  been  noted  that  the  essential  peculiarity  of  the 
cell  is  that  it  possesses  certain  properties  which  are  characteristic 
of  Hfe.  By  this  is  meant  that  a  cell  is  able:  i.  To  nourish  itself  and 
to  grow — metabolism.  2.  To  do  its  own  particular  work  in  the  body 
economy — specialfunction.  3.  To  respond  to  stimulation — irritability. 
4.  To  move — motion.     5.  To  produce  other  cells — reproduction. 

As  would  be  expected,  these  properties,  existing  as  they  do  in 
Kving  cells,  cannot  always  be  sharply  separated  but  frequently  over- 
lap. Thus,  e.g.,  in  the  muscle  cell  "motion"  equals  "special  func- 
tion." 

In  the  simplest  forms  of  animal  Hfe,  where  a  single  cell  constitutes 
the  entire  individual,  all  of  these  functions  are  performed  by  the  one 
cell.  In  all  higher,  that  is,  multicellular  animals,  there  are  not  only 
many  cells  but  many  kinds  of  cells,  and  this  morphological  differen- 
tiation corresponds  to  a  physiological  differentiation,  each  group  of 
cells  developing  along  certain  well-defined  Hnes  for  the  performance 
of  its  own  special  function. 

I.  Metabolism. — This  term  is  used  to  designate  those  cellular 
activities  which  have  to  do  with  the  nutrition  of  the  cell.  A  cell  is 
able  (i)  to  take  up  from  without  substances  suitable  for  its  nutri- 
tion and  to  transform  these  into  its  own  pecuHar  structure,  and  (2) 
to  dispose  of  the  waste  products  of  intracellular  activities.  The 
former  is  known  as  constructive  metabolism  or  anabolism,  the  latter  as 
destructive  metabolism  or  katabolism. 

It  is  possible,  for  example,  to  watch  an  amceba  send  out  projections 
(pseudopodia)  (see  p.  52)  around  an  adjacent  bit  of  food  material. 
These  projections  coalescing  finally  completely  enclose  the  food 
material  within  the  body  of  the  amoeba  where  it  is  acted  upon  by 
the  protoplasm  in  such  a  way  (digested)  as  to  completely  lose  its 
identity  and  to  finally  become  an  integral  part  of  the  cytoplasm. 

There  is  normally  maintained  within  the  cell  a  state  of  equi- 
librium between  this  constructive  and  destructive  metaboHsm,  be- 
tween the  intake  of  food  on  the  one  hand  and  the  outflow  of  material 
products  or  of  energy  on  the  other.  Stated  as  an  equation,  intake 
=  outgo.  Any  marked  -f-  or  —  on  one  side  of  the  equation 
without  corresponding  +  or  —  on  the  other  side  must  disturb  this 
equilibrium  and  must  result  in  physical  changes  within  the  cell. 
Thus  any  marked  +  in  intake  without  corresponding  -|-  in  outgo 


THE  CELL  51 

must  result  in  growth  of  the  cell,  while  any  +  in  outgo  without  corre- 
sponding +  in  intake  must  tend  toward  diminution  in  bulk  of  cell 
and  final  destruction. 

2.  Special  Function. — Tliis  is  the  special  work  which  it  is  the  part 
of  the  cell  to  perform.  It  varies  greatly  for  different  cells.  Some 
cells,  as,  e.g.,  the  surface  cells  of  the  skin,  appear  to  act  mainly  as  pro- 
tection for  more  delicate  underlying  structures.  Other  cells — gland 
cells— in  addition  to  maintaining  their  own  nutrition,  produce 
specific  substances  (secretions),  which  are  of  great  importance  to  the 
body  as  a  whole.  Still  other  cells,  e.g.,  nerve  cells  and  muscle  cells, 
have  the  power  to  store  up  their  food  substances  in  such  a  way  as  to 
make  them  available  in  the  form  of  energy.  This  appears  to  be 
accomphshed  by  the  building  up  within  the  cell  of  highly  complex 
and,  consequently,  unstable  molecular  combinations.  By  reduction 
of  these  unstable  combinations,  molecules  of  greater  stability  and 
less  complexity  are  formed.  This  results  in  the  transformation  of 
potential  into  kinetic  energy,  and  the  expenditure  of  this  energy  is 
expressed  in  function. 

3.  Irritability  is  that  property  which  enables  a  cell  to  respond  to 
external  stimuli.  Cells  vary  in  respect  to  their  irritability,  the  most 
markedly  irritable  cells  in  higher  animals  being  those  of  the  neuro- 
muscular mechanism.     Stimulation  may  be  mechanical,  electrical. 


/j^ 


Fig.  6. — Amoeboid  Movement.     Successive  changes  in  shape  and  position  of 
fresh-water  amoeba. 

thermal,  chemical,  etc.  The  response  of  the  cell  to  certain  forms  of 
chemical  stimulation  is  known  as  chemotaxis.  Some  substances 
attract  cells  (positive  chemotaxis);  others  repel  cells  (negative 
chemotaxis) .  Stimuli  other  than  chemical  possess  similar  properties, 
as  indicated  by  the  terms  thermotaxis,  galvanotaxis,  etc.  Some  cells 
are  so  specialized  as  to  react  only  to  certain  kinds  of  stimulation,  e.g., 
the  retinal  cells  only  to  light  stimuli. 

4.  Motion. — This  is  dependent  wholly  ujion  the  protoplasm  of  the 
cell,  and  is  exhibited  in  several  somewhat  different  forms. 


52 


THE  CELL 


(a)  Amcehoid  Movement.  This  consists  in  the  pushing  outward 
by  the  cell  of  processes  (pseudopodia) .  These  may  be  retracted  or 
may  draw  the  cell  after  them.  In  this  way  the  cell  may  change  both 
its  shape  and  position  (Fig.  6) .  White  blood  cells  exhibit  to  a  marked 
degree  the  power  of  amoeboid  movement. 

{h)  Protoplasmic  Movement.  This  occurs  wholly  within  the  lim- 
its of  the  cell,  changing  neither  its  shape  nor  position.  It  occurs  in 
both  plant  and  animal  cells,  and  consists  of  a  sort  of  circulation  or 
"  streaming  "  of  the  protoplasm.  It  is  evidenced  by  the  movement  of 
minute  granules  present  in  the  protoplasm,  by  changes  in  the  position 
of  the  nucleus,  etc. 

(c)  Ciliary  Movement.  This  is  the  whipping  motion  possessed 
by  little  hair-like  processes  called  cilia,  which  project  from  the  sur- 
faces of  some  cells. 

Certain  cells  which  are  specialized  for  the  particular  purpose  of 
motion  as,  e.g.,  muscle  cells,  possess  such  powers  of  contraction  that 
they  are  able  to  move  not  only  themselves  but  other  parts  with  which 

they  are  connected.  This 
power  of  contractility  is  de- 
pendent upon  the  spongio- 
plasm,  the  hyaloplasm  play- 
ing a  more  passive  role.  In 
muscle  cells  the  highly  de- 
veloped contractile  powers 
appear  to  be  due  to  the  ex- 
cessive development  and 
peculiar  arrangement  of  the 
spongioplasm. 

5.  Reproduction.  —  The 
overthrow  of  the  long-held 
biological  fallacy  of  sponta- 
neous generation  was  soon 
followed  by  the  downfall  of  a  similar  theory  regarding  the  origin  of 
cells.  We  now  know  that  all  cells  are  derived  from  cells,  and  that 
the  vast  number  and  complex  of  cells  which  together  form  the  adult 
human  body  are  all  derived  from  a  single  primitive  cell,  the  ovum. 

Reproduction  of  cells  takes  place  in  two  ways,  by  direct  cell 
division  or  amitosis,  and  by  indirect  cell  division  or  mitosis.  In  both 
amitosis  and  mitosis  the  division  of  the  cell  body  is  preceded  by  divi- 
sion of  the  nucleus. 


Fig.  7. — Epithelial  Cells  ftom  Ovary  of 
Cockroach,  Showing  Nuclei  Dividing  Amitot- 
ically.     (Wheeler.) 


THE  CELL 


53 


Direct  Cell-division — Amitosis  (Figs.  7  and  8).- — In  this  form  of 
cell-division  the  nucleus  divides  into  two  daughter  nuclei  without  any 
apparent  prehminary  changes  in  its  structure.  The  division  of  the 
nucleus  may  or  may  not  be  followed  by  division  of  the  cell  body,  in  the 
latter  case  resulting  in  the  formation  of  polynuclear  cells.  This  form 
of  cell-division  is  uncommon  in  higher  animals  where  Flemming  con- 
siders it  a  degenerative  phenomenon  rather  than  a  normal  method 
of  cell-increase.  It  is  a 
common  method  of  cell- 
division  in  the  protozoa. 

Indirect  Cell-dr^- 
siox — Mitosis  (Figs.  9, 
10). — In  this  form  of  cell- 
division  also,  the  nucleus 
divides  into  two  daughter 
nuclei,  and  the  cell  into 
two  daughter  cells,  but 
only  after  they  have 
passed  through  certain 
characteristic  and  compli- 
cated changes.  These 
changes  occur  as  a  contin- 
uous process,  but  it  is  con- 
venient for  clearness  of 
description  to  arbitrarily 
divide  them  into  stages  or 

phases.  Thus  we  recognize  in  mitosis:  (a)  the  prophase;  (b)  the 
metaphase;  {c)  the  anaphase;  (d)  the  telophase.  The  prophase  is 
the  stage  of  preparation  on  the  part  of  the  nucleus  for  division; 
the  metaphase,  the  actual  separation  of  the  nuclear  elements;  the 
anaphase,  the  formation  of  the  two  daughter  nuclei;  the  telophase, 
the  reconstruction  of  the  two  daughter  resting  nuclei  and  the  divi- 
sion of  the  cytoplasm. 

(a)  The  Prophase  (Fig.  9,  B,  C,  D)  is  marked  by  the  following 
changes : 

I.  The  centrosome,  if  single,  divides  into  two  daughter  centro- 
somes.  In  most  actively  dividing  cells,  hpwever,  the  centrosome 
is  at  this  stage  already  double  (Fig.  9,  A)  having  divided  as  early, 
frequently,  as  the  anaphase  of  the  preceding  mitosis. 

The  two  daughter  centrosomes,  each  surrounded  by  its  attraction 


\ 
\ 
\ 

jzr 

Fig.  8. — Epithelial  cell  from  bladder  showing 
amitotic  division  of  its  nucleus.  (Nemileff.)  /, 
Cj'toplasm;  //,  two  daughter  nuclei;  ///,  fibrils 
uniting  daughter  nuclei. 


54 


THE  CELL 


sphere,  now  move  apart  but  remain  connected  by  fibrils,  probably 
derived  from  the  linin  (Fig.  g,  B).  These  fibrils  form  the  central  or 
achromatic  spindle.  Two  other  sets  of  fibrils  radiate  from  each  cen- 
trosom^one,  known  as  the  polar  rays,  passes  out  toward  the  periph- 
ery of  the  cell;  the  other,  known  as  the  mantle  fibres,  extends  from  the 
centrosome  to  the  chromosomes  (Fig.  g,  C).  The  two  centrosomes 
with  their  fibres  constitute  the  amphiaster. 


Fig.  9. — Diagrams  of  Successive  Phases  of  Mitosis. 

A,  Resting  cell,  with  reticular  nucleus  and  true  nucleolus;  c,  attraction  sphere  with 
two  centrosomes. 

B,  Early  prophase.  Chromatin  forming  continuous  thread — the  spireme;  nucleolus 
stiU  present;  a,  amphiaster;  the  two  centrosomes  connected  by  iibrils  of  achromatic 
spindle. 

C,  Later  prophase.  Segmentation  of  spireme  to  form  the  chromosomes;  achromatic 
spindle  connecting  centrosomes;  polar  rays;  mantle  fibres;  fading  of  nuclear  membrane. 

D,  End  of  prophase.  Monaster — mitotic  figure  complete;  ep,  chromosomes  ar- 
ranged around  equator  of  nucleus;  fibrils  of  achromatic  spindle  connecting  centrosomes; 
mantle  fibres  passing  from  centrosomes  to  chromosomes.  (E.  B.  Wilson,  "The  Cell," 
The  MacmiUan  Co.) 

2.  During  or  immediately  following  the  formation  of  the  amphi- 
aster, important  changes  take  place  in  the  nucleus.  It  increases  in 
size  and  loses  the  reticular  appearance  of  the  resting  nucleus,  its 
chromatic  elements  becoming  arranged  in  a  long  spireme-thread  or  in 
several  shorter  threads,  the  closed  skeinjor  closed  spireme.     This  next 


THE  CELL  55 

becomes  thicker  and  more  loosely  arranged,  thus  forming  the  open 
spireme.  That  some  chemical  as  well  as  morphological  change  has 
taken  place  in  the  transformation  of  the  reticulum  of  the  resting 
nucleus  into  the  spireme  is  shown  by  the  marked  increase  in  staining 
intensity,  the  spireme  taking  a  much  darker  stain  than  the  reticulum. 
Late  in  the  prophase  the  nucleolus  and  nuclear  membrane  disappear. 
The  cytoplasm  and  karyoplasm  then  become  continuous  and  both 
spireme  and  amphiaster  lie  free  in  the  general  cell  protoplasm  (Fig. 
9,  C). 

3.  The  spireme  next  breaks  up  into  a  number  of  segments — 
chromosomes  (Fig.  9,  C).  These  are  usually  rod-shaped  at  first, 
later  they  may  become  U's  or  V's  or  may  even  become  spheroidal. 
The  chromosomes  now  arrange  themselves  regularly  around  the  equa- 
tor of  the  nucleus,  their  closed  ends  being  directed  centrally. 

The  details  of  the  transformation  of  the  reticulum  into  chromo- 
somes vary.  In  some  cases  a  single  spireme-thread  is  formed.  In 
others  the  spireme-thread  first  splits  longitudinally  into  two  threads 
before  segmenting  into  chromosomes.  Again  the  spireme-thread 
may  show  segmentation  into  chromosomes  from  the  beginning. 
In  still  other  cases  the  chromosomes  apparently  form  directly  from 
the  reticulum  without  the  intervention  of  the  spireme  stage.  It  is 
most  important  to  note  that  while  the  number  of  chromosomes 
varies  for  different  species  of  plants  and  animals,  it  is  fixed  and 
characteristic  for  a  given  species.  Thus  in  Ascaris  megalocephala 
(much  used  for  study  on  account  of  its  small  number  of  chromosomes) 
the  number  is  4,  in  the  mouse  24,  in  man,  estimated  by  some  as  16, 
by  others  24.^  This  means  that  whenever  mitosis  occurs  in  Ascaris, 
the  spireme-thread  invariably  segments  into  4  chromosomes.  Chro- 
mosomes and  amphiaster  now  constitute  the  mitotic  figure  which  at 
this  stage  is  known  as  the  monaster,  its  formation  marking  the  end 
of  the  prophase. 

{h)  Metaphase  (Fig.  10,  E).  This  marks  the  beginning  of  actual 
division  of  the  nucleus.  Each  chromosome  splits  longitudinally 
(longitudinal  cleavage)  into  two  daughter  chromosomes,  each  contain- 

»  Gayer  (Biol.  Bui.  Marine  Biol.  Lab.  Wood's  Hole,  Mass.,  Vol.  XIX)  describes 
twenty-two  chromosomes  in  human  spermatogonia,  of  which  two  are  "accessory". 
Apparently  *half  the  resulting  spermatids  contain  ten  chromosomes,  the  other  half 
twelve,  two  of  which  aie  accessory.  In  Syromastes  Wilson  found  an  identical  condi- 
tion and  it  was  later  determined  that  the  somatic  number  of  chromosomes  for  Syro- 
mastes was  twenty-two  for  the  male  and  twenty-four  for  the  female.  Guyer  concludes 
that  the  probable  somatic  number  for  the  human  male  is  twenty-two,  for  the  female 
twenty-four. 


56 


THE  CELL 


ing  exactly  one-half  the  chromatin  of  the  parent  chromosome.  U- 
and  V-shaped  chromosomes  always  begin  to  spHt  at  the  apex,  from 
which  point  the  separation  extends  to  the  open  ends. 

(c)  Anaphase  (Fig.  lo,  F,  G). — An  equal  number  of  daughter 
chromosomes  now  travels  along  the  fibrils  of  the  achromatic  spindle — 
apparently  under  the  influence  of  the  mantle  fibres — toward  each 
daughter  centrosome  around  which  they  become  grouped.     In  this 


Fig.  io. — Diagrams  of  Successive  Phases  of  Mitosis. 

E,  Metaphase.  Longitudinal  cleavage;  splitting  of  chromosomes  to  form  daughter 
chromosomes,  ep;  n,  cast-off  nucleolus. 

F,  Anaphase.  Daughter  chromosomes  passing  along  fibrils  of  acromatic  spindle 
toward  centrosomes;  division  of  centrosomes;  if,  interzonal  fibres  or  central  spindle. 

G,  Late  anaphase.    Formation  of  diaster;  beginning  division  of  cell  body. 

H,  Telophase.  Reappearance  of  nuclear  membrane  and  nucleolus;  two  complete 
daughter  cells,  each  containing  a  resting  nucleus.  (E.B.Wilson,  "The  Cell,"  The 
Macmillan  Co.) 

way  are  formed  two  daughter  stars,  the  mitotic  figure  being  known 
at  this  stage  as  the  diaster  (Fig.  lo,  G).  These  daughter  stars  are  at 
first  connected  by  the  fibrils  of  the  achromatic  spindle.  In  this 
stage  may  also  occur  beginning  division  of  the  cell  body.  In  actively 
dividing  cells  each  centrosome  frequently  undergoes  division  at  this 
stage,  resulting  in  four  centrosomes  to  the  cell. 

{d)  Telophase  (Fig.  lo,  E). — This  is  marked  by  division  of  the 


THE  CELL  57 

cell  protoplasm  and  consists  of  a  cycle  of  changes,  by  means  of  which 
each  group  of  daughter  chromosomes  is  transformed  into  the  chro- 
matin network  of  a  resting  nucleus.  These  changes  are  the  same 
as  those  described  in  the  prophase,  but  occur  in  the  reverse  order,  the 
chromosomes  uniting  to  form  the  spireme,  and  the  spireme  becoming 
transformed  into  the  nuclear  network.  The  result  is  the  formation 
of  two  daughter  cells.  The  nuclear  membrane  reappears,  as  does  also 
the  nucleolus.  Each  daughter  cell  is  thus  provided  with  a  resting 
nucleus.  The  fact  that  the  number  of  chromosomes  which  enter 
into  the  formation  of  the  chromatic  reticulum  of  the  nucleus  of  each 
daughter  cell  is  the  same  as  the  number  into  which  the  spireme  of 
the  parent  cell  dixdded,  has  suggested  the  hypothesis  that  the  chro- 
mosomes maintain  their  identity  even  during  the  resting  stage. 

The  time  required  for  the  mitotic  process  is  usually  from  one-half 
to  three-quarters  of  an  hour.  Exceptionally  it  is  prolonged  to  several 
hours. 

The  role  which  each  part  of  the  cell  plays  in  the  vital  activities  of  the  cell, 
and  the  physiological  correlation  of  these  various  parts,  have  been  but  partially- 
determined.  Experiments  upon  some  of  the  protozoa  show  that  if  the  cell  be 
divided  into  two  parts,  one  part  containing  the  nucleus,  the  other  part  non- 
nucleated,  the  behavior  of  the  two  parts  is  very  different.  The  part  contain- 
ing the  nucleus  soon  again  becomes  a  complete  cell  with  all  the  properties  which 
the  cell  originally  possessed.  The  non-nucleated  part  responds  somewhat  to 
stimulation,  is  capable  of  some  movement,  makes  some  feeble  attempts  at 
digestion,  but  is  incapable  of  secretion,  of  reconstructing  the  complete  cell,  of 
reproduction,  and  soon  dies.  Even  when  a  small  part  of  the  nucleus  remains 
in  the  cut-off  piece  of  cytoplasm  reconstruction  may  take  place.  On  the  other 
hand  a  nucleus  completely  deprived  of  its  cytoplasm  is  incapable  of  reconstructing 
the  cell.  In  Infusoria  each  cell  has  two  nuclei,  a  macro-nucleus  and  a  micro- 
nucleus,  the  former  connected  with  nutrition,  the  latter  with  reproduction. 
These  facts  together  with  the  behavior  of  the  nucleus  during  the  ingestion  of 
food,  during  secretion,  and  even  during  motion,  warrant  the  belief  that  while 
in  all  probability  most  of  the  actual  work  of  the  cell  takes  place  in  the 
cytoplasm,  the  nucleus  exerts  a  more  or  less  controlling  influence  over  all  cell 
activities. 

The  parts  which  the  several  cell  structures  play  in  mitosis  have  been  the 
subjects  of  much  study  and  are  as  yet  not  fully  determined. 

As  to  the  behavior  of  the  chromatic  portion  of  the  mitotic  figure  little  doubt 
exists.  It  originates  in  the  chromatic  portion  of  the  nuclear  reticulum  of  the 
parent  cell  and  its  destination  is  the  chromatic  portion  of  the  reticulum  of  the 
daughter  cells. 

The  r6le  of  the  ccntrosome  in  mitosis  is  not  so  clear.  It  has  been  called  the 
"dynamic  centre"  of  the  cell  because  in  most  cases  it  appears  to  be  the  active 
agent  in  initiating  and  probably  further  directing  the  mitotic  process.     The 


58  THE  CELL 

origin  of  the  astral  fibres  is  not  always  the  same.  In  Infusoria  the  centrosome 
is  found  within  the  nucleus  and  both  amphiaster  and  chromosomes  are  of  nu- 
clear origin.  In  some  of  the  higher  plants  the  amphiaster  is  derived  wholly 
from  the  spongioplasm.  In  the  egg  cells  of  Echinoderm,  part  of  the  amphiaster 
(central  spindle)  is  of  nuclear,  the  remainder  (asters)  of  cytoplasmic  origin. 
That  the  centrosome  is  not  always  the  active  factor  in  mitosis  is  shown  by  the 
fact  that  in  the  higher  plants  no  centrosome  can  be  demonstrated  during  any 
stage  of  mitosis,  and  also  that  in  some  cases  the  chromosomes  divide  without 
previous  division  of  the  centrosome.  Between  mitotic  periods  the  centrosome 
with  or  without  its  aster  may  remain  as  an  integral  part  of  the  resting  cell.  It 
may,  on  the  other  hand,  entirely  disappear  during  the  resting  stage. 

Branca  calls  attention  to  the  fact  that  the  centrosome  is  an  organ  of  no  "con- 
stancy, permanence,  or  specificity,"  that  (i)  in  certain  cells  it  is  impossible  to 
demonstrate  a  centrosome  at  any  time;  (2)  that  when  a  centrosome  has  been 
demonstrated  for  a  certain  type  of  cell,  it  cannot  always  be  found  even  in  that 
type  of  cell;  (3)  that  certain  parts  of  the  centrosome,  the  rays,  are  cytoplasmic, 
while  another  part,  the  centriole,  reacts  like  nuclear  material  (chromatin). 
He  concludes  that  the  centrosome  is  a  portion  of  the  protoplasm  '"  temporarily 
differentiated  for  a  specific  function;  not  unlike  the  basal  filaments  which  appear 
temporarily  in  gland  cells  when  they  become  active,  both  being  functional  forms 
of  protoplasm  which  can  succeed  each  other  as  the  cell  changes  the  character 
of  its  function." 

It  is  through  the  above-described  process  of  cell-division  that  new 
cells  are  produced  to  replace  those  worn  out  as  a  result  of  their  labors 
or  destroyed  by  injury.  It  is  through  the  same  process  that  the  vast 
number  of  cells  which  make  up  the  adult  body  are  developed  from 
one  original  cell — the  ovum.  Such  powers  of  evolution  are  not, 
however,  inherent  in  the  ovum  itself,  but,  in  sexual  reproduction, 
are  acquired  only  after  its  union  with  germinal  elements  from  the 
male.  This  union  of  male  and  female  germinal  elements  is  known  as 
fertilization  of  the  ovum. 

Fertilization  or  the  Ovum 

Prior  to  and  in  preparation  for  fertilization,  both  male  and  female 
cells  must  pass  through  certain  changes.  These  are  known  as  matu- 
ration of  the  spermatozoon  on  the  male  side  (p.  344)  and  of  the  ovum  on 
the  female  (p.  357). 

The  spermatozoon  (Fig.  11)  is  developed  from  a  cell  of  the  sem- 
iniferous tubule  of  the  testis.  The  nucleus  of  this  cell  so  divides  its 
chromosomes  that  each  spermatozoon  contains  just  one-half  the  num- 
ber of  chromosomes  characteristic  of  cells  of  the  species.  These  are 
contained  in  the  head  of  the  spermatozoon,  which  thus  represents  the 


THE  CELL 


59 


nucleus  of  the  male  sexual  cell,  the  middle  piece  probably  containing 
the  centrosome,  the  tail  piece  the  remains  of  the  protoplasm. 

The  nucleus  of  the  ovum  or  germinal  vesicle  also  passes  through  a 
series  of  changes  by  which  it  loses  one-half  its  chromosomes.  The 
germinal  vesicle  or  nucleus  of  the  ovum  first  undergoes  mitotic 
division  with  the  usual  longitudinal  cleavage  of  its  chromosomes  and 
the  formation  of  two  daughter  nuclei.  One  of  these  and  its  centrosome 
are  extruded  from  the  cell  as  the  first  polar  body. 
The  remaining  nucleus  and  centrosome  again  divide 
mitotically,  only  in  this  second  division,  instead  of 
the  usual  longitudinal  cleavage  of  chromosomes,  by 
which  each  daughter  nucleus  is  provided  with  the 
same  number  of  chromosomes  as  the  mother  nucleus, 
the  chromosomes  simply  separate,  one-half  going  to 
each  daughter  nucleus.  One  of  the  daughter  nuclei 
and  its  centrosome  are  now  extruded  as  the  second 
polar  body.  The  polar  bodies  ultimately  disappear, 
as  does  also  the  centrosome  remaining  within  the 
egg.  This  leaves  in  the  now  matured  ovum  a  single 
nucleus,  which  is  known  as  the  female  pronucleus, 
and  which  contains  one-half  the  number  of  chromo- 
somes characteristic  of  cells  of  the  species. 

During  this  process  in  some  animals — in  others 
after  its  completion — the  spermatozoon  enters  the 
ovum.      The    head  of   the   spermatozoon  becomes   man  Spermatozoa. 

,  ,  ,  1  -1  11         •  1  (After      Retzius.) 

the  male  pronucleus,   the  middle  piece    becomes  a    i,  Head  seen  on 
centrosome,  while  the  tail  is,  in  some  instances  at        '  ?'     f\^*^T 

'  '  on  edge;  k,  head; 

least,  left  behind  as  the  spermatozoon  enters  the  w,  body;/,  tail;  e, 
egg.  The  chromatin  of  the  male  next  becomes 
arranged  as  chromosomes.  Male  and  female  pronuclei  now  lose 
their  limiting  membranes  and  approach  each  other,  their  chromo- 
somes intermingling.  As  each  pronucleus  contained  one-half  the 
number,  the  monaster  thus  formed  contains  the  full  number  of 
chromosomes  characteristic  of  the  species.  Meanwhile  the  male 
centrosome,  formed  from  the  body  of  the  spermatozoon,  divides 
into  two  daughter  centrosomes.  These  with  their  radiating  fibrils 
have  the  same  arrangement  relative  to  the  monaster  of  mingled 
male  and  female  chromosomes,  already  described  under  mitosis. 
By  longitudinal  cleavage  of  these  chromosomes,  as  in  ordinary 
mitosis,  two  sets  of   daughter  chromosomes  are  formed.     Each  set 


60  ' 


THE  CELL 


passes  along  the  filaments  of  the  achromatic  spindle  to  its  centro- 
some.  Thus  is  formed  the  Master.  By  continuation  of  the  mitotic 
process  two  new  nuclei  are  formed,  each  nucleus  containing  the 
number  of  chromosomes  characteristic  of  the  species,  and  each  being 


female    pronu- 
cleus 


head    of    sper- 
-  matozoon  with 
centrosome 


centrosome 


male  pronu 

7"~    cleus 


female  pro- 
nucleus 


\        chromosome  of  female       / 
^i--   pronucleus  ' 


chromosome  of  male 
"'  pronucleus 


centrosome 


chromosome 
.  - '    from  female 

'•-,'.■','•  ^.-'/         pronucleus 

( O^  U  .'         chromosom.e 

•"^s  ./---Vl^.   from  male 
7         pronucleus 


centrosome 


Fig.  12 — Diagram  of  Fertilization  of  the  Ovum.  (The  somatic  number  of  chro- 
mosomes being  four.)  (From  Bohm  and  von  Davidoff,  after  Boveri. 
I,  Ovum  surrounded  by  spermatozoa,  only  one  of  which  is  in  the  act  of  penetration. 
Toward  the  latter  the  protoplasm  of  the  ovum  sends  out  a  process;  2,  Head  of  spermato- 
zoon has  entered  ovum,  its  body  becoming  the  male  centrosome,  its  tail  having  disap- 
peared; 3,  The  head  of  spermatozoon  has  become  the  male  pronucleus.  Male  and 
female  pronuclei  approach  each  other.  Between  them  is  the  (male)  centrosome; '''4, 
The  spiremes  of  male  and  female  pronuclei  have  each  formed  two  chromosonaes.  The 
centrosome  has  divided;  5,  Male  and  female  chromosomes  have  mingled  and  by  longitu- 
dinal cleavage  (see  Mitosis,  p.  53)  have  become  eight.  These  become  arranged  in  the 
equatorial  plane  of  the  ovum.  Mantle  fibres  extend  from  centrosomes  to  chromosomes; 
6,  Division  of  the  ovum;  two  daughter  cells,  each  containing  a  daughter  nucleus.  Each 
daughter  nucleus  contains  four  chromosomes,  two  derived  from  each  pronucleus. 


THE  CELL 


61 


made  up  equally  of  male  and  female  chromosome  ele?nents.  Thus 
occurs  the  first  division  of  the  fertilized  ovum  into  two  daughter 
cells.     By  similar  mitotic  processes  these  two  cells  become  four,  the 


SEGMENTA- 
TION   CAVITY. 


Fig,   13. — Segmentation  of  the  Ovum.     (From  Gcrrish,  after  van  Beneden.) 
a,  Two-cell  stage  resulting  from  first  division  of  fertilized  ovum;  b,  four-cell  stage; 
c,  d,  e,  later  stages.     A,  Differentiation  into  inner  and  outer  cells;  B,  Formation  of 
segmentation  cavity;  C,  Embryonic  vesicle,  showing  two  primary  germ  layers.     Outer 
cells,  ectoderm;  inner  cells,  entoderm. 


62 


THE  CELL 


four  cells  become  eight,  etc.     This  is  known  as  segmentation  of  the 
ovum. 

The  earlier  generations  of  these  cells  are  morphologically  alike 
and  are  known  as  hlastomeres.  Soon,  however,  these  cells  become 
spread  out  and  at  the  sam.e  time  differentiated  into  two  primary 
germ  layers.  The  outer  of  these  is  known  as  the  ectoderm  or  epiblast, 
the  inner  as  the  entoderm  or  hypoblast.  Between  these  two  layers 
and  derived  from  them  a  third  layer  is  formed,  the  mesoderm  or  meso- 
blast.     These  three  layers  constitute  the  blastoderm. 


^m 


mm?. 


Fig.  14. — ^The  Two  Primary  Germ  Layers;  from  transverse  section  through  primitive 
groove  of  a  chick  of  27  hours' incubation,  a,  Ectoderm  (outer  germ  layer);  b,  ento- 
derm (inner  germ  layer);  c,  mesoderm  (middle  germ  layer);  d,  anlage  of  notochord. 

As  to  vi^hat  determines  and  controls  fertilization,  comparatively  little  is 
known.  As  in  ordinary  mitosis,  the  origin  of  the  centrosome  is  obscure.  In 
some  forms,  at  least,  the  centrosome  of  the  spermatid  enters  into  the  formation 
of  the  middle  piece  of  the  spermatozoon.  The  male  centrosome  thus  enters  the 
ovum.  It  is  also  knovsrn  that  in  some  eggs  the  egg-centrosome  disappears  soon 
after  the  extrusion  of  the  second  polar  body,  and  that  the  centrosome  of  the  fer- 
tilized egg  develops  in  close  relation  to  the  middle  piece  of  the  spermatozoon. 
These  facts  point  to  the  male  centrosome  as  the  centrosome  of  fertilization. 

The  ovum  and  spermatozoon  are  apparently  brought  together  by  a  definite 
attraction  on  the  part  of  the  ovum  toward  the  spermatozoon.  The  nature  of 
this  attraction  is  unknown.  It  is  possibly  chemical,  and  is  exerted  only  be- 
tween ova  and  spermatozoa  of  the  same  species.  This  has  been  proved  for  lower 
forms  by  mixing  ova  of  one  species  and  spermatozoa  from  several  species  in  an 
inert  medium  when  only  spermatozoa  of  the  same  species  will  attach  themselves 
to  the  ova.  That  the  attractive  force  lies  in  the  cytoplasm  is  shown  by  the  fact 
that  small  pieces  of  the  egg  protoplasm  free  from  nuclear  elements  will  exert 
sufi&cient  powers  to  cause  spermatozoa  to  enter  them. 

As  to  the  point  of  entrance  of  the  spermatozoon,  some  eggs  may  be  entered 
at  any  point,  others  are  permeable  at  but  one  point. 

One  spermatozoon  only  is  required  for  fertilization,  and  when  this  sper- 
matozoon has  entered,  the  egg  apparently  loses  its  power  of  attracting  sper- 
matozoa, or  else  develops  some  actual  defense  against  further  entrance  of 
spermatozoa. 


THE  CELL  63 


TECHNIC 


1.  Fresh  cells  may  be  studied  by  gently  scraping  the  surface  of  the  tongue, 
transferring  the  mucus  thus  obtained  to  a  glass  slide  and  covering  with  a  cover- 
glass. 

2.  Red  blood  cells  from  the  frog  are  prepared  as  foUows:  After  killing  the 
frog  the  heart  is  opened  and  the  blood  allowed  to  drop  into  a  tube  containing 
Hayem's  fluid  (sodium  chlorid  i  gm.,  sodium  sulphate  5  gm.,  mercuric  chlorid 
0.5  gm.,  distilled  water  ico  c.c).  After  shaking,  the  cells  are  allowed  to  settle 
for  from  twelve  to  twenty-four  hours.  The  fixative  is  then  replaced  by  water, 
the  tube  again  shaken,  the  cells  allowed  to  settle,  and  the  water  is  replaced  with 
80  per-cent.  alcohol  tinged  with  iodin.  After  from  twelve  to  twenty-four  hours 
the  alcohol  is  decanted  and  the  tube  partly  filled  with  alum-carmine  solution 
(page  19).  About  twenty-four  hours  usually  sufiices  for  staining  the  nuclei. 
The  alum-carmine  is  then  poured  ofif  and  the  cells  well  shaken  in  water.  After 
settling,  the  water  is  replaced  by  glycerin,  to  which  a  small  amount  of  picric 
acid  has  been  added.  In  this  the  cells  may  be  permanently  preserved.  The 
nuclei  are  stained  red  by  the  carmine,  the  cytoplasm  yellow  by  the  picric  acid. 

3.  Surface  cells  from  the  mucous  membrane  of  the  bladder.  The  bladder 
is  removed  from  a  recently  killed  animal,  pinned  out  mucous  membrane  side 
up  on  a  piece  of  cork  and  floated,  specimen  side  down,  on  equal  parts  MiiUer's 
fluid  and  Ranvier's  alcohol  (technic,  4,  p.  7,  and  a,  p.  4)  for  from  twenty-four 
to  forty-eight  hours.  The  specimen  is  then  washed  in  water  and  the  cells  re- 
moved by  gently  scraping  the  surface.  These  may  then  be  stained  and  pre- 
served in  the  same  manner  as  the  preceding.  Cells  from  the  different  layers 
should  be  studied;  also  the  appearance  of  the  large  surface  cells  seen  on  flat  and 
on  edge,  showing  pitting  of  under  surface  by  cells  beneath. 

4.  Amoeboid  movejuent  may  be  studied  by  watching  fresh-water  amoebae  or 
white  blood  cells.  A  drop  of  water  containing  amoebae  is  placed  on  a  slide, 
covered,  and  a  brush  moistened  with  oil  is  passed  around  the  cover  to  prevent 
evaporation.  The  activity  of  the  amoebae  may  be  increased  by  slightly  raising 
the  temperature.  An  apparatus  known  as  the  warm  stage  is  convenient  for 
demonstrating  amoeboid  movement.  A  drop  of  blood,  human,  or  better  from 
one  of  the  cold-blooded  animals,  may  be  used  for  the  study  of  amoeboid  move- 
ment in  the  white  blood  cells.  It  should  be  placed  on  a  slide,  covered,  and 
immediately  examined  on  the  warm  stage. 

5.  Ciliary  movement  is  conveniently  studied  by  removing  a  small  piece  of 
the  gill  of  an  oyster  or  mussel,  teasing  it  gently  in  a  drop  of  normal  salt  solution 
and  covering.  The  cilia  being  very  long,  their  motion  may  be  easily  studied, 
especially  after  it  has  become  slow  from  loss  of  vitality. 

6.  Mitosis.  The  salamander  tadpole  and  the  newt  are  classical  subjects 
for  the  study  of  cell-division.  The  female  salamander  is  usually  full  of  embryo 
tadpoles  in  January  and  February.  The  embryos  are  removed  and  fixed  in 
Flemming's  fluid  (technic  7,  p.  7),  after  which  they  may  be  preserved  in  equal 
parts  of  alcohol,  glycerin,  and  water.  Mitotic  figures  may  be  found  in  almost 
any  of  the  tissues.  Pieces  of  cpiflermis  from  the  end  of  the  tail,  the  parietal 
peritoneum,  and  bits  of  the  gills  arc  especially  satisfactory.     If  the  newt's  tail 


64  THE  CELL 

is  used,  it  should  be  fixed  in  the  same  manner,  embedded  in  paraffin  and  cut 
into  thin  sections.  These  are  stained  with  Heidenhain's  haematoxylin,  technic 
3,  p.  i8. 

Certain  vegetable  tissues,  such  as  the  end  roots  of  a  young,  rapidly  growing 
onion  or  magnoHa  buds,  are  excellent  for  the  study  of  mitosis.  The  technic  is 
the  same  as  for  animal  tissues. 

General  References  for  Fvirther  Study  of  the  Cell 

Branca,  A.:  Histologie,  Paris,  1906. 

Conklin,  E.  G.:  Karyokinesis  and  Cytokinesis,  Jour.  Acad.  Nat.  Sci.  of 
Phila.,  vol.  xii,  1902. 

Harper,  E.  H.:  The  Fertilization  and  Early  Development  of  the  Pigeon's 
Egg.     Amer.  Jour,  of  Anat.,  vol.  iii,  No.  4,  1904. 

Hertwig,  O.:  Die  Zelle  und  die  Gewebe,  1898. 

Hertwig,  R.:  Eirife,  Befruchtung  u.  Furchungsprozess.  In  Hertwig's  Hand- 
buch  d.  vergleich.  u.  experiment.  Entwickelungslehre  der  Wirbeltiere,  Bd.  I,  Teil 
I,  1903. 

Lillie,  F.  R. :  A  Contribution  toward  an  Experimental  Analysis  of  the  Karyo- 
kinetic  Figure.     Science,  New  Series,  vol.  xxvii,  1908. 

McMurrich:     The  Development  of  the  Human  body. 

Minot:  Human  Embryology.     A  Laboratory  Text-book  of  Embryology. 

Sobotta,  J.:  Die  Befruchtung  u.  Furchung  des  Eies  der  Maus.  Arch.  f.  mik. 
Anat.,  Bd.  xlv,  1895. 

Wilson,  E.  B.:  The  Cell  in  Development  and  Inheritance,  2d  ed.,  1900. 


PART  III 
THE  TISSUES 


CHAPTER  I 
HISTOGENESIS— CLASSIFICATION 

Ectoderm,  mesoderm,  and  entoderm  (see  page  62)  are  known 
as  the  primary  layers  of  the  blastoderm.  They  differ  from  one  an- 
other not  only  in  position,  but  also  in  the  structural  characteristics 
of  their  cells.  The  separation  of  the  blastomeres  into  these  three 
layers  represents  the  first  morphological  differentiation  of  the  cells 
of  the  developing  embryo.  By  further  and  constantly  increasing 
dift'erentiation  are  developed  from  these  three  primary  layers  all 
tissues  and  organs,  each  layer  giving  rise  to  its  own  special  group  of 
tissues.  The  tissue  derivations  from  the  primary  layers  of  the  blasto- 
derm are  as  follows: 

Ectoderm.^ — (i)  Epithehum  of  skin  and  its  appendages — hair, 
nails,  sweat,  sebaceous  and  mammary  glands,  including  smooth 
muscle  of  sweat  glands. 

(2)  Epithelium  of  mouth  and  anus,  of  glands  opening  into  mouth, 
and  enamel  of  teeth. 

(3)  Epithelium  of  nose  and  of  glands  and  cavities  connected  with 
nose. 

(4)  Epithelium  of  external  auditory  canal  and  of  membranous 
labyrinth. 

(5)  Epithelium  of  anterior  surface  of  cornea,  of  conjunctiva,  of 
crystalline  lens,  of  lacrymal  gland,  and  of  lacrymal  canal. 

(6)  Epithelium  of  male  urethra,  except  prostatic  portion. 

(7)  Epithehum  of  medulla  of  suprarenals,  of  pineal  bodies,  of 
pituitary  body  and  of  a  few  other  small  ductless  glands. 

(8)  Entire  nervous  system,  including  retina  and  its  forward 
extension  over  iris,  also  muscle  tissue  of  sphincter  and  dilator  pupillae. 

Entoderm,  (i)  Epithelium  of  digestive  tract  (excepting  mouth 
and  its  glands  and  anus,)  and  of  glands  connected  with  digestive 
tract  including  liver,  gall  bladder  and  pancreas. 

(2)  Epithelium  of  respiratory  tract  and  of  its  glands. 

(3)  Epithelium  of  bladder  except  the  trigonum,  of  female  urethra, 
of  vaginal  vestibule  and  glands  of  Bartholin,  of  prostatic  portion  of 
male  urethra,  prostatic  glands  and  glands  of  Cowper. 

67 


(68  THE  TISSUES 

(4)  Epithelium  of  tympanum  and  of  Eustachian  tube. 

(5)  EpitheHum    of    thyreoid   and    parathyreoid,    reticulum   of 
thymus,  and  Hassall's  corpuscles. 

Mesoderm. — (i)  All  the  connective  or  supporting  tissues  except 
neuroglia. 

(2)  Lymphatic  organs  with  the  exception  of  Hassall's  corpuscles 
and  reticulum  of  the  thymus. 

(3)  Blood  cells  and  bone-marrow. 

(4)  Striated,  cardiac  and  smooth  muscle  (with  the  possible  excep- 
tion of  smooth  muscle  of  sweat  glands  and  of  iris) . 

(5)  Endothelium  lining  blood-vessels  and  lymphatics. 

(6)  MesotheHum  lining  serous  membranes — pleura,  pericardium, 
and  peritoneum. 

(7)  Epithelium  of  genito-urinary  system  with  the  exception  of  the 
urethra  and  a  large  part  of  the  bladder. 

(8)  Epithelium  of  the  suprarenal  cortex. 

In  all  but  the  lowest  forms  of  animal  life  the  body  consists  of  an 
orderly  arrangement  of  many  kinds  of  cells.  From  the  cells  is  de- 
veloped a  substance  which  lies  outside  the  cells  and  is  known  as  inter- 
cellular substance.  This  may  be  small  in  amount,  just  sufficient  to 
unite  the  cells,  as  in  epithelium,  or  it  may  so  predominate  as  to  deter- 
mine the  character  of  the  tissue,  as  in  some  forms  of  connective  tissue. 
It  does  not  always  completely  separate  the  cells  which  may  be  con- 
nected across  the  intercellular  substance  by  extensions  of  their 
protoplasm,  as  in  the  "intercellular  bridges"  of  epithelium  or  the 
anastomosing  processes  of  connective-tissue  cells.  Less  commonly 
cells  are  united  in  such  a  multinuclear  continuum  that  their  bound- 
aries are  almost  or  wholly  lost.  Such  a  structure  is  known  as  a  syncy- 
tium. The  association  of  a  particular  type  of  cell  with  a  particular 
type  of  intercellular  substance  is  known  as  a  tissue.  The  character 
of  a  tissue  depends  upon  the  character  of  its  cells,  of  its  intercellular 
substance,  and  their  relations  to  each  other.  Further  differentiation 
of  cells  and  intercellular  substance  within  a  particular  tissue  gives 
rise  to  various  sub-groups  of  the  tissue.  The  association  of  tissues 
to  form  a  definite  structure  for  the  performance  of  a  particular 
function  is  known  as  an  organ.  The  physiological  association  of 
organs  constitutes  a  system.  The  fact  that  chemical  changes  take 
place  in  intercellular  substance  as  well  as  in  cells  has  led  to  the  sug- 
gestion that  the  intercellular  substance  is  endowed  with  the  same 


HISTOGENESIS— CLASSIFICATION  69 

vital  properties  as  the  cell.  The  consensus  of  opinion  is,  however, 
that  the  intercellular  substance  is  derived  originally  from  the  cell, 
is  replenished  by  the  cell,  is  dependent  upon  the  cell  for  its  nourish- 
ment, and  is  incapable  of  activity  or  existence  apart  from  the  cell. 

A  scientific  classification  of  the  tissues  is  at  present  impossible. 

The  foregoing  list  of  tissue  derivations  shows  how  unsatisfactory 
is  any  attempt  at  classification  on  the  basis  of  histogenesis,  many 
tissues  which  are  morphologically  similar  being  derived  from  two 
or  even  all  three  of  the  blastodermic  layers. 

The  following  is  the  usual  classification  of  adult  tissues:  (i)  Epithe- 
hal  tissues;  (2)  connective  tissues;  (3)  blood;  (4)  muscle  tissue;  (5) 
nerve  tissue. 

Of  these,  epithelium  and  connective  tissue  may  be  regarded  as  the 
more  elementary  tissues,  being  common  to  both  plants  and  animals. 
Blood  is  sometimes  classified  among  the  connective  tissues.  Muscle 
and  nerve  are  the  most  highly  specialized  tissues  and  are  pecuhar 
to  animals.  While  the  individuality  of  the  tissues  classified  is 
recognized,  the  physiological  necessities  of  nutrition,  innervation,  etc., 
scarcely  permit  the  existence  of  any  one  tissue  alone  by  itself.  Thus 
blood  and  blood  vessels  permeate  almost  all  tissues  except  epithelium, 
while  the  latter  is  everywhere  traversed  by  elements  of  nerve  tissue. 


CHAPTER  II 

EPITHELIUM  (INCLUDING  MESOTHELIUM  AND 
ENDOTHELIUM) 

General  Characteristics. — Epithelium  is  derived  from  all  three 
germ  layers.  It  consists  almost  wholly  of  cells.  The  intercellular 
substance  is  merely  sufficient  to  attach  the  cells  to  one  another  and  is, 
consequently,  known  as  cement  substance.  A  characteristic  of  this 
cement  substance  is  its  reaction  to  silver  nitrate  (Figs.  15,  26,  27). 
In  some  instances  the  protoplasm  of  adjacent  epithelial  cells  is  seen 
to  be  even  more  closely  associated,  the  intervening  cement  substance 
being  bridged  over  by  delicate  processes  of  protoplasm  which  pass 
from  one  cell  to  another  and  are  known  as  'intercellular  bridges" 
(see  Fig.  19,  p.  74).  It  seems  probable  that  the  minute  spaces  be- 
tween the  processes  serve  as  channels  for  the  passage  of  food  (lymph) 
to  the  cells.  Reference  to  Figs.  155  and  187  shows  that  a  precipitation 
of  silver  also  occurs  in  some  tubules  filled  with  glandular  secretions. 
It  is  possible  that  the  so-called  intercellular  cement  may  be  of  the 
nature  of  an  intercellular  lymph.  The  surface  cells  of  epithelium 
are  united  by  continuous  cement  substance  in  which  there  are  appar- 
ently no  spaces.     In  this  way  escape  of  lymph  is  prevented. 

Epithelial  cells  vary  in  size  and  shape,  the  element  of  pressure 
being  a  frequent  determining  factor.  They  are  often  extremely 
elastic,  allowing  great  changes  in  shape  and  relation.  Thus  the 
epithelium  of  the  collapsed  bladder  is  thick  and  the  cells  columnar, 
but  as  the  bladder  fills,  the  cells  become  flatter  until  in  complete 
distention  the  epithelium  is  thin  and  consists  of  flattened  cells. 
Their  protoplasm  may  be  clear,  finely  or  coarsely  granular,  or  pig- 
mented. Each. cell  usually  contains  a  single  well-defined  nucleus. 
Two  or  more  nuclei  are  sometimes  present.  Some  epitheHal  cells 
are,  when  fully  matured,  non-nucleated,  e.g.,  respiratory  epithelium 
of  lung. 

When  epithehum  rests  upon  connective  tissue,  it  is  usually  sepa- 
rated from  the  latter  by  a  thin,  apparently  homogeneous  membrane 
known  as  the  basal  membrane  or  membrana  propria.     Authorities 

70 


EPITHELIUM  71 

differ  as  to  whether  this  membrane  is  of  connective-tissue  or  of 
epithehal  origin. 

Surface  epithehal  cells  frequently  have  thickened  free  borders  or 
cuticulcB,  which  unite  to  form  a  continuous  membrane,  the  cuticular 
memhrane.  Striations  extend  from  the  cytoplasm  into  the  cuticulae. 
A  still  greater  speciaHzation  of  the  surface  of  the  cell  is  seen  in  the 
cihated  cell.  In  this  cell  fine  hair-hke  projections — cilia — extend 
from  the  surface  of  the  cell. 

Some  epithehal  cells  show  important  changes  dependent  upon 
their  functional  activities.  An  example  of  this  is  seen  in  the  mucous 
cell  in  which  there  is  a  transformation  of  the  greater  part  of  the  cyto- 
plasm into,  or  its  replacement  by,  mucus. 

EpitheHa  are  devoid,  as  a  rule,  of  both  blood-  and  lymph-vessels. 
An  exception  to  this  is  the  stria  vascularis  of  the  cochlea.  Nerves, 
on  the  other  hand,  are  abundant. 

Classification. — EpitheHa  may  be  classified  according  to  shape 
and  arrangement  of  cells  as  follows: 

(i)  Simple  EpitheHum. — {a)  Squamous;  {h)  columnar. 

(2)  Stratified  EpitheUum. — (a)  Squamous;  {h)  columnar. 

(3)  MesotheHum  and  Endothehum. 

Speciahzations  of  the  above-mentioned  types  are  known  as:  {a) 
Cihated  epithehum;  {h)  pigmented  epithehum:  (c)  glandular  epithe- 
hum;  {d)  neuro-epithelium. 

Pigment  may  occur  in  any  type  of  epithehum.  Ciha  are  found 
only  in  the  simple  columnar  and  stratified  columnar  forms. 

I .  Simple  Epithelium 

In  simple  epithehum  the  cells  are  arranged  in  a  single  layer. 

{a)  Simple  squamous  epithelium  consists  of  flat  scale-hke  cells 
which  are  united  by  an  extremely  small  amount  of  intercellular  sub- 
stance. The  edges  of  the  cells  are  smooth  or  serrated.  Seen  on 
flat,  they  present  the  appearance  of  a  mosaic.  Seen  on  edge,  the 
cells  appear  fusiform,  being  thickest  at  the  center,  where  the  nucleus 
is  situated,  and  thinning  out  toward  the  periphery.  Simple  squa- 
mous epithehum  has  but  a  limited  distribution  in  man.  It  occurs 
in  the  lungs  as  non-nucleated  respiratory  epithelium,  in  Bowman's 
capsule  of  the  renal  corpuscle,  in  the  descending  arm  of  Henle's  loop 
of  the  urinifcrous  tubule,  in  the  retina  in  the  form  of  pigmented  cells, 
and  on  the  posterior  surface  of  the  anterior  lens  capsule. 

{h)  Simple  columnar  epithelium  consists  of  a  single  layer  of  elon- 


72 


THE  TISSUES 


gated  cells.  The  bases  of  the  cells  are  usually  separated  from  the 
underlying  connective  tissue  by  a  basement  membrane.  The 
nucleus  is,  as  a  rule,  in  the  deeper  part  of  the  cell,  near  the  basement 
membrane.     Many  of  these  cells  have  prominent  thickened  free 


Fig.  15.— From  Section  of  Cat's  Lung,  stained  with  silver  nitrate,  showing  out- 
lines of  the  Simple  Squamous  Epithehum  Lining  the  Air  Vesicle,  a,  Two  epithelial 
cells;  h,  the  wavy  stained  intercellular  substance;  c,  foetal  cells;  d,  connective  tissue. 

borders  or  cuticulas.  This  form  of  epithelium  is  often  ciliated.  The 
height  of  the  cell  varies  greatly,  there  being  all  gradations  from  high 
columnar  to  low^cuhoidal.     Simple  columnar  epithelium  lines  the 


^ 


Fig.  16.  — Simple  Columnar  Epithelium  from  the  Human  Small  Intestine,  a 
Mucous  (goblet)  cell;  b,  basement  membrane;  c,  thickened  free  border  (cuticula)' 
d,  leucocyte  among  the  epithelial  cells;  e,  replacing  cell. 

gastro-intestinal  canal,  the  uriniferous  tubule  (excepting  the  descend- 
ing arm  of  Henle's  loop),  simple  tubular  glands,  the  ducts  of  some 
compound  tubular  glands,  the  smaller  bronchi,  the  membranous 
and  penile  portions  of  the  male  urethra,  and  the  gall-bladder. 


EPITHELIUM 


73 


In  simple  columnar  epithelium,  in  addition  to  the  single  row  of 
epithelial  cells,  there  are  found  lying  near  the  basement  membrane, 
between  the  bases  of  the  epithelial 
cells,  small,  spherical,  or  irregular 
cells,  which  frequently  show  mitosis 
and  which  are  known  as  replacing 
cells.  They  appear  to  develop 
into  columnar  epithehal  cells  as 
they  are  needed  to  replace  older 
cells.  The  so-called  psendo-strati- 
fied  epithelium  is  a  form  of  simple  columnar  epithelium,  in  which, 
from  crowding  of  the  cells,  the  nuclei  have  come  to  lie  at  different 
levels,  thus  giving  the  appearance  of  stratification  (Fig.  17). 


Fig.  17.  — Diagram  of  Pseudostratified 
Epithelium,  showing  Nuclei  situated  at 
Different  Levels. 


2.  Stratified  Epithelium 

In  stratified  epithelium  the  cells  are  arranged  in  more  than  one 
layer. 

(a)  Stratified  squamous  epithelium  is  developed  from  simple 
epithelium  by  the  growth  of  new  cells  between  the  old  cells  and  the 
underlying  connective  tissue.     It  consists  of   several  layers  of  cells 


Flat  surface  cells     C^?^ 


■-i:j 


^?5^' 


"^ 


Polyhedral  cells  , 


'Ml... 


^ 


•^ 


Cuboidal  eel! 


i?' 


ii? 


rj,  A-. 


m 


Fig.  18. — Stratified  Squamous  Epithelium  from  Cat's  Oesophagus. 

which  vary  greatly  in  size  and  shape.  The  surface  cells  are  large  and 
flat.  Beneath  these  are  several  layers  of  polyhedral  cells,  with  often 
very  distinct  protoplasmic  intercellular  connections  ("intercellular 
bridges,"  see  also  p.  74).     The  deepest  cells  are  columnar  or  cuboi- 


74 


THE  TISSUES 


dal.  It  is  thus  seen  that  in  stratified  squamous  epithelium  only  the 
surface  cells  are  squamous.  This  form  of  epithelium  rests  upon  a 
more  or  less  distinct  basement  membrane, 
which  is  frequently  thrown  up  into  folds  by 
papillae  of  the  underlying  connective  tissue. 
Stratified  squamous  epithelium  forms  the 
surface  of  the  skin  and  of  mucous  membranes 
of  cavities  opening  upon  it,  mouth  and 
oesophagus,  conjunctiva,  external  ear,  vagina 
and  external  sheath  of  hair  follicle. 

(b)  Stratified  Columnar  Epithelium. — 
Only  the  surface  cells  are  columnar,  the 
deeper  cells  being  irregular  in  shape.  The 
surface  cells  frequently  send  long  processes 
down  among  the  underlying  cells.  The  free 
surface  is  often  marked  by  a  well-developed 
cuticula.  Some  epithelia  of  this  type  are  ciliated.  Stratified 
columnar  epithelium  is  found  in  the  larynx,  nose,  palpebral  con- 


Fig.  19. — Epithelial  Cells 
from  the  Stratum  Spinosum 
of  the  Human  Epidermis 
showing  "Intercellular 
Bridges."  X700.  (Szymo- 
nowicz.) 


— ^-w^ 


:  ^) 


^i' 


.^1 


Fig.  20. — Transitional  Epithelium  from  the  Human  Bladder. 

junctiva,  largest  of  the  gland  ducts,  the  vas  deferens,  and  part  of 
the  male  urethra. 


Fig.  21.— Stratified  Columnar  Epithelium  from  the  Human  Male   Urethra.     X400, 


Stratified  epithelium  composed  of  only  from  three  to  six  layers  of 
cells    is    sometimes    designated    ''transitional    epithelium.''     This 


EPITHELIUM 


75 


type  of  epithelium  usually  rests  upon  a  basement  membrane  free  from 
papillae.  The  surface  cells  are  large  and  frequently  contain  two  or 
three  nuclei.  Their  free  surfaces  are  flat,  while  their  under  surfaces 
show  depressions  due  to  pressure  from  underlying  cells.     The  deeper 


'P^^^nilUU  JWii^^''^*W)iljij4^  -"^.-.iy 


-^ 


\'-Y 


Fig.   22. — Stratified   Columnar  Ciliated  Epithelium  from  the  Human  Trachea.     A 
mucous  (goblet)  cell  also  is  present. 

cells  are  polygonal  or  irregularly  cuboidal.  This  form  of  epithelium 
lines  the  bladder,  ureter,  pelvis  of  the  kidney,  and  prostatic  portion  of 
male  urethra. 


% 
Fig.  23.— Isolated  Ciliated  Cells  and  Goblet  Cells  from  Dog's  Trachea.     X700. 

Modified  Forms  of  Epithelium 

(a)  Ciliated  Epithelium. — In  this  form  of  epithelium,  fine  hair-like 
processes — cilia — extend  from  the  surface  of  the  cell.  These  cilia 
vary  from  twelve  to  twenty-five  for  each  cell  and  may  be  short  as  in 


76 


THE  TISSUES 


the  trachea  or  long  as  in  the  epididymis.  There  is  usually  a  well- 
defined  cuticula  from  which  the  cilia  appear  to  spring.  According 
to  Apathy,  the  ciHa  extend  through  the  cuticula,  giving  to  the  latter  a 
striated  appearance  (Fig.  24).  Just  beneath  the  cuticula  each  cilium 
shows  a  swelling — the  basal  granule.  Lenhossek  considers  these 
granules  centrosomes.  The  intracellular  exten- 
sions of  the  ciha  converge  toward  the  nucleus, 
and  are  continuous  with  the  reticular  or  fibrillar 
structure  of  the  cell  body.  The  motion  of  cilia 
is  wave-like,  the  wave  always  passing  in  the  same 
direction.  Various  explanations  of  ciliary  motion 
have  been  given.  It  has  been  suggested  that  it  is 
due  to  the  contractile  powers  of  the  spongioplasm, 
also  that  it  is  due  to  changes  in  surface  tension  of 
the  film  of  protoplasm  which  covers  each  cilium. 


Fig.  24.  Fig.  25. 

Fig.  24. — Ciliated'Epithelial  Cell  from  Intestine  of  MoUusk  (Engelmann),  showing 
a,  cuticula,  h,  basal  granules,  and  c,  intracellular  extensions  of  cilia. 

Fig.  25. — Pigmented  Epithelial  Cells  from  the  Human  Retina  (X350),  showing 
different  degrees  of  pigmentation.  The  clear  spots  in  the  centres  of  the  cells  represent 
the  unstained  nuclei. 

Cilia  are  confined  to  the  surface  cells  of  simple  columnar  and 
stratified  columnar  epithelium. 

Simple  columnar  ciliated  epithelium  occurs  in  the  smaller  bronchi, 
uterus,  Fallopian  tubes  and  central  canal  of  the  spinal  cord. 

Stratifie'd  columnar  ciliated  epithelium  occurs  in  large  bronchi, 
trachea,  larynx,  nose.  Eustachian  tube,  vas  deferens  and  epididymis. 

(&)  Pigmented  epithelium  consists  of  cells  the  cytoplasm  of  which 
contains  brown  or  black  pigment.  It  is  usually  present  in  the  form 
of  spherical  or  rod-like  granules.  Examples  of  it  are  seen  in  the 
pigmented  epithelium  of  the  retina  and  in  the  pigmented  cells  of  the 
deeper  layers  of  the  epidermis  in  colored  races  (Fig.  25). 


EPITHELIUM  77 

(c)  Glandular  Epithelium.- — This  forms  the  essential  or  secreting 
element  of  glands  and  is  mostly  of  the  simple  cylindrical  variety. 
The  different  kinds  of  glands  and  their  epithelia  will  be  described 
among  the  organs. 

{d)  N euro-epithelium. — This  is  a  highly  specialized  form  of  epithe- 
lium which  occurs  in  connection  with  the  end  organs  of  nerves,  under 
which  heading  it  will  be  described. 

3.  Mesothelium  and  Endothelium 

While  recognizing  the  present  tendency  toward  considering  those 
tissues  formerly  classified  as  endothelium,  as  simple  squamous  epithe- 
lium, the  correctness  of  the  newer  classification  still  remains  suh 
judice  and,  so  long  as  this  is  the  case,  we  prefer  to  retain  the  certainly 


Fig.  26. — Mesothelium  from  Omentum  of  Dog  Treated  according  to  Technic  7,  p. 
79-  X3S0.  Black  wavy  lines  indicate  the  intercellular  cement  substance.  The 
mesothelial  cells  cover  the  strands  of  connective  tissue,  the  fibres  of  the  latter  being 
visible  through  the  transparent  cell  bodies. 

much  more  convenient  classification  of  Minot,  which  coincides  with 
his  subdivision  of  the  mesoblast.  According  to  this  classification  for 
those  tissues  which  resemble  epitheHum  in  structure  and  which  are 
derived  from  the  sublayer  of  the  mesoderm  which  he  designates  the 
mesenchyme,  the  term  endothelium  is  retained.  The  term  mesothe- 
lium is  used  for  those  tissues  which  resemble  epithelium  but  are  de- 
rived from  a  subdivision  of  the  mesoderm  which  he  designates  the 
mesothelial  layer. 


78  THE  TISSUES 

Mesothelium  and  endothelium  are  similar  in  structure.  Each 
consists  of  thin  flattened  cells  with  clear  or  shghtly  granular  proto- 
plasm and  bulging  oval  or  spherical  nuclei.  The  edges  of  the  cells 
are  usually  wavy  or  serrated.  The  cells  are  united  by  an  extremely 
small  amount  of  intercellular  "cement"  substance,  which  is  usually 
indistinguishable  except  by  the  use  of  a  special  technic. 


Fig.  27. — The  Endothelium  of  a  Small  Blood-vessel.     Silver  nitrate  stain.     X350. 

/' 
Endothelium  forms  the  walls  of  the  blood  and  lymph  capillaries 

and  Hnes  the  entire  blood-vessel  and  lymph-vessel  systems. 

Mesothelium  lines  the  body  cavities — the  pleura,  the  pericardium 

and  the  peritoneum. 

Recent  researches  make  it  seem  probable  that  the  surface  cells 

of  serous  membranes  are  modified  connective-tissue  cells  rather  than 

epithelium. 

TECHNIC 

1.  Simple  Squamous  Epithelium. — That  of  the  lung  may  be  demonstrated 
by  injecting  with  silver  solution  (technic  i,  p.  28)  through  a  bronchus  and  then 
immersing  the  tissue  in  the  same  solution.  The  lungs  of  young  kittens  furnish 
especially  satisfactory  material. 

2.  Simple  Columnar  Epithelium. — ^A  piece  of  small  intestine,  human  or 
animal,  is  pinned  out  flat  on  cork  and  fixed  in  formalin-Muller's  fluid  (technic 
5,  p.  7).  Sections  are  cut  perpendicular  to  the  surface,  stained  with  haematoxy- 
lin  and  eosin  (technic  i,  p.  20)  and  mounted  in  glycerin  tinged  with  eosin  (p. 
22).  Little  processes  known  as  villi  project  from  the  inner  surface  of  the  intes- 
tine. These  are  covered  by  a  single  layer  of  columnar  epithelial  cells.  The 
cuticulae  and  cuticular  membrane  are  usually  well  shown.  Among  the  simple 
cylindrical  cells  are  seen  large  clear  or  slightly  blue-stained  cells.  These  are 
known  from  their  secretion  as  mucous  cells,  from  their  shape  as  goblet  cells,  and 
are  classed  as  modified  epithelium  of  the  glandular  type.  These  should  be  stud- 
ied in  their  various  stages  of  secretion,  from  the  cell  in  which  only  a  small  amount 
of  mucus  is  present  near  the  outer  margin,  to  the  cell  whose  protoplasm  is  almost 
wholly  replaced  by  mucus.  Some  cells  will  be  found  in  which  the  surface  has 
ruptured  and  the  mucus  can  be  seen  pouring  out  of  the  cell. 


EPITHELIUM  79 

3.  Stratified  Squamous  Epithelium. — The  cornea  furnishes  good  material 
for  the  study  of  stratified  squamous  epithelium.  An  eye  is  removed  from  a 
freshl}'  killed  animal  and  the  cornea  cut  out  and  fixed  in  formalin-Miiller's 
fluid.  Sections  are  cut  perpendicular  to  the  surface,  and  treated  as  in  the  pre- 
ceding. The  cells  are  laid  down  in  from  six  to  eight  layers.  The  oesophagus 
may  be  used  instead  of  the  cornea,  its  mucous  membrane  being  lined  by  a  some- 
what thicker  epithelium. 

4.  Transitional  Epithelium. — This  is  conveniently  studied  in  the  mucous 
membrane  of  the  bladder.     Technic  same  as  2,  above. 

5.  Stratified  Columnar  Epithelium. — A  portion  of  trachea  from  a  recently 
killed  animal  is  treated  according  to  the  same  technic.  The  surface  cells  are 
cUiated  so  that  this  specimen  also  serves  to  demonstrate  that  type  of  modified 
epithelium.  Isolated  cells  or  clumps  of  cells  may  be  obtained  from  the  trachea 
in  the  manner  described  in  technic  3,  p.  63. 

6.  Pigmented  Epithelium. — Fix  a  freshly  removed  eye  in  formalin-Miiller's 
fluid  (p.  7).  After  hardening,  cut  transversely  and  remove  the  vitreous  and 
retina.  The  pigmented  cells  remain  attached  to  the  inner  surface  of  the  chorioid, 
and  may  be  removed  by  gently  scraping.  They  may  be  preserved  and  mounted 
in  glycerin. 

7.  jMesothelium. — Part  of  the  omentum  of  a  recently  killed  animal  is  removed 
and  washed  in  water,  care  being  taken  not  to  injure  the  tissue  in  handling.  The 
water  is  then  replaced  by  a  i  to  500  aqueous  solution  of  silver  nitrate.  After 
half  an  hour  the  specimen  is  removed  from  the  silver,  washed  in  water,  transferred 
to  80-per-cent.  alcohol  and  placed  in  the  sunlight  until  it  becomes  light  brown 
in  color.  It  is  then  preserved  in  fresh  80-per-cent.  alcohol.  The  nuclei  may  be 
stained  with  hsematoxylin  (stain  5,  p.  18).  The  specimen  should  be  mounted 
in  glycerin.  Wavy  black  lines  indicate  the  intercellular  cement  substance.  The 
nuclei  of  the  mesothelial  cells  are  stained  blue,  those  of  the  underlying  connec- 
tive-tissue cells  a  paler  blue.  It  must  be  borne  in  mind  in  studying  this  specimen 
that  the  strands  or  trabeculae  of  the  omentum  are  not  composed  of  mesothelium, 
but  of  fibrous  connective  tissue,  and  that  the  flat  mesothelial  cells  merely  lie 
upon  the  surface  of  the  connective-tissue  strands. 

8.  Endothelium  may  be  demonstrated  by  removing  the  bladder  from  a 
recently  killed  frog,  distending  it  with  air  and  subjecting  it  to  the  same  technic. 
By  this  means  the  intercellular  substance  of  the  endothelium  of  the  blood-vessels 
of  the  bladder  wall  is  stained  and  the  outlines  of  the  cells  are  thus  shown. 


CHAPTER  III 
THE  CONNECTIVE  TISSUES 

Under  this  head  are  classified  Connective  Tissue  Proper,  Carti- 
lage, and  Bone. 

General  Characteristics. — The  most  prominent  characteristic  of 
the  connective  tissues  is  the  predominance  of  the  intercellular  sub- 
stance. In  this  respect  the  connective  tissues  differ  markedly  from 
epithehum.  Moreover  it  is  the  intercellular  substance  and  not 
the  cells  which  determines  the  physical  character  of  the  tissue. 
Thus,  for  example,  the  hardness  of  bone  and  teeth,  the  firmness  and 
elasticity  of  cartilage,  the  toughness  of  tendon,  the  softness  of  sub- 
cutaneous connective  tissue,  are  all  due  to  the  character  and  arrange- 
ment of  the  intercellular  elements.  In  most  forms  of  supportive  tissue 
the  cellular  elements  are  very  similar  and  in  no  way  determine  the 
physical  character  of  the  tissue. 

The  role  of  the  connective  tissues  is  mainly  passive,  and  the 
cells,  instead  of  playing  the  most  active  part,  as  in  epitheUal,  muscle 
and  nerve  tissues,  serve  mainly  for  the  maintenance  of  the  nutrition 
of  the  more  important  intercellular  substance.  The  latter  thus 
predominates  in  function  as  well  as  in  quantity,  its  character  accord- 
ing with  the  specific  function  of  the  tissue.  Thus,  where  strength 
and  preservation  of  form  are  essential,  are  found  connective  tissues 
with  such  intercellular  substance  as  occurs  in  bone;  where  softness 
and  flexibiHty  are  required,  such  loosely  arranged  intercellular 
elements  as  are  present  in  areolar  tissue. 

Most  of  the  connective  tissues  are  extremely  vascular,  differing 
also  in  this  respect  from  epithelium.  An  exception  to  this  rule 
is  hyaHn  cartilage. 

All  of  the  connective  tissues  have  a  com.mon  origin  in  the  more 
loosely  arranged  portion  of  the  mesoderm  which  is  known  as  the 
mesenchyme. 

A  very  close  relation  exists  between  the  different  forms  of  con- 
nective tissue  as  evidenced  by  a  marked  tendency  and  ability  of 
one  form  to  be  closely  united  to,  or  to  be  transformed  into,  or  to  be 

80 


THE  CONNECTIVE  TISSUES  81 

replaced  by,  another  form.  This  may  be  progressive  in  line  of  de- 
velopment or  retrogressive  in  line  of  degeneration.  For  example 
the  close  physical  union  which  exists  between  tendon  and  bone  or 
between  cartilage  and  bone  or  tendon:  or  the  manner  in  which 
the  forms  of  bone  are  first  laid  down  in  connective  tissue,  which  is 
replaced  by  bone,  or  by  cartilage  followed  by  bone.  Again  in  the 
callus  which  occurs  in  the  uniting  of  fractures,  there  is  first  fibrous 
tissue,  then  bone,  or  there  may  be  an  intervening  cartilaginous  stage, 
or  repair  may  fail  of  completion,  leaving  permanent  connective 
tissue  or  cartilage. 

The  correlation  of  the  dift'erent  forms  of  connective  tissue  is 
also  shown  by  the  fact  that  in  difi'erent  species  the  same  anatomical 
structure  is  sometimes  formed  by  different  members  of  the  group. 
Thus  in  some  birds  the  leg  tendons  are  formed  of  bone,  while  in 
certain  fish  the  skeletal  system  is  cartilaginous.  In  Mammals  the 
sclera  of  the  eye  is  fibrous  connective  tissue.  In  Batrachians  the 
same  structure  is  cartilage,  in  Birds,  bone. 

Classification: — 

[  (i)  Embryonal   ^  («)  loose  or  areolar 
I                                 I  (fat     tissue,     pig- 

ry  ^-       -T-  (2)  Fibrillar        \         merited  tissue) 

Connective  Tissue  (6)  t endon-aponeu- 

[   Hj^alin        (3)  Elastic  ^ 

Cartilage    ]  Fibrous   [   (4)  Reticular 

[  Elastic 
Bone 


Connective  Tissue 


The  mesenchyme  consists  at  first  wholly  of  small  spheroidal  or  ovoid  cells 
These  cells  proliferate  and  elaborate  a  substance  which  separates  the  cells  from 
one  another  and  is  the  primitive  ground  or  intercellular  substance.  As  the 
cells  separate  they  assume  irregular  stellate  branching  forms  and  anastomose 
to  form  a  network  or  syncytium.  Such  a  tissue  is  known  as  mucous  or  embryonal 
connective  tissue  (Fig.  28),  is  found  in  the  adult  only  in  the  umbilical  cord  and 
possibly  in  the  vitreous  of  the  eye,  but  in  the  embryo  is  widely  distributed. 
With  the  exceptions  notfed  it  represents  but  a  stage  in  the  development  of  the 
more  specialized  forms  of  connective  tissue. 

Portions  of  this  embryonal  connective  tissue  develop  fibres  in  the  ground 
substance.  Some  of  these  fibres  are  known  as  white  or  fibrillated  fibres  or,  be- 
cause of  their  chemical  constitution,  as  collagenous  fibres.  Others  are  known 
as  yellow  or  elastic  fibres  and  consist  of  elastin.  This  differentiation  of  the 
ground  substance  gives  rise  to  connective-tissue  proper.  At  other  points 
in  the  mesenchyme,  cartilaginous  material  appears  in  the  ground  substance. 
These  points  are  numerous  and  widely  separated  and  each  represents  a  chondri- 
fication  center  or  point  of  development  of  cartilage.  At  some  points  in  the  con- 
6 


82  THE  TISSUES 

nective  tissue  or  in  the  cartilage  there  are  depositions  of  lime  salts  in  the  ground 
substance — calcification.  This  is  followed  by  the  formation  of  true  bone — 
ossification. 

Regarding  the  development  of  the  connective-tissue  fibrils,  there  are  two 
theories:  (i)  According  to  one,  they  are  developed  directly  from  the  protoplasm 
of  the  connective-tissue  cells.  The  cells  increase  in  length,  and  fine  granules 
appear,  which  arrange  themselves  in  rows  in  the  cytoplasm;  these  granules  unite 
to  form  fibrils.  Such  cells  are  known  as  fibroblasts,  and  their  fibrils  are  the  fore- 
runners of  the  intercellular  fibrils  of  connective  tissue.  A  modification  of  this 
theory  derives  the  fibrils  from  the  peripheral  portion  of  the  cell — the  exoplasm. 
(2)  According  to  the  other  theory  the  fibrils  are  developed  from  the  matrix, 
minute  granules  first  becoming  arranged  in  rows  and  later  uniting  to  form 
fibrils. 

Regarded  as  opposing  theories,  there  is  in  reality  but  little  antagonism  be- 
tween them.  There  is  no  doubt  as  to  the  intercellular  matrix  being  a  product 
of  the  cell.  Whichever  theory,  therefore,  is  accepted,  the  entire  intercellular 
substance,  fibres  and  ground  substance  are  ultimate  derivatives  of  the  cell. 
Recent  studies,  especially  those  of  Mall,  are  confirmatory  of  the  second  of  the 
theories  given  above.  He  maintains  that  the  connective-tissue  fibrils,  both 
white  and  elastic,  are  derivatives  of  an  active  intercellular  matrix,  which  latter 
is  a  direct  product  of  the  cell. 

Two  similar  theories  exist  as  to  the  development  of  elastic  fibres,  a  cellular 
theory  and  an  extracellular  theory.  According  to  some  advocates  of  the  cell- 
ular theory,  the  elastic  fibres  are  derived  from  the  exoplasm;  according  to  others, 
from  the  cytoplasm  immediately  surrounding  the  nucleus.  Recent  researches 
favor  the  extracellular  theory.  Mall  describes  extremely  minute  fibrils  in  the 
ground  substance,  which  later  develop  into  elastic  fibres. 

CONNECTIVE  TISSUE  PROPER 

{Mucous  Tissue-Gelatinous  Tissue) 

EMBRYONAL  CONNECTIVE  TISSUE 

This  is  the  least  differentiated  of  the  connective  tissues  and  has 
been  already  partly  described  (p.  81).  It  occurs  only  in  the  foetus. 
It  consists  of  irregular  stellate,  branching  cells  which  anastomose, 
and  are  irregular}^  scattered  through  an  apparently  structureless 
ground  substance  rich  in  mucin  (Fig.  28). 

FIBRILLAR  CONNECTIVE  TISSUE 

Fibrillar  connective  tissue,  also  known  as  white  fibrous  tissue  or 
connective  tissue  proper,  consists  of  cells  and  fibres  lying  in  a  basement 
or  ground  substance.  The  elements  of  fibrillar  tissue  may  be  class- 
ified as  follows: 


THE  CONNECTIVE  TISSUES 


83 


I.  Fixed 


Cells 


[     (a)  Ordinary  connective-tissues  cells. 
J     (b)  Plasma  cells. 
1     (c)  Mast  cells. 
[     (d)  Clasmatocytes 
2.  Wandering. 


Intercellular  substance 


(a)  Fibres 


white  or  fibrillated, 
yellow  or  elastic. 


(b)  Ground  or  basement  substance. 


fl' 


\/C 


I 


/Y> 


Fig.  28. — Mucous  Connective  Tissue  from  Umbilical    Cord  of  Eight-inch  Foetal 
Pig.     X600.     At  this  stage  the  ground  substance  shows  some  fibrillat:':)n. 


Connective -tissue  Cells. — (a)  The  ordinary  fixed  connective- 
tissue  cell  is  often  the  only  connective-tissue  cell  seen  in  ordinary 
sections.  It  is  an  irregular  shaped  cell,  often  quite  flattened 
with  clear  or  slightly  granular  cytoplasm,  and  an  oval  nucleus. 
(Figs. 29  and  30.)  In  loosely  arranged  tissue  when  the  cells  are 
well  separated,  the  cell  is  usually  stellate  with  many  branches, 
which  anastomose  with  branches  of  neighboring  cells.  In  a  dense 
tissue  such  as  the  cornea,  these  cells  apparently  lie  in  little  cell 
spaces  or  lacunar  from  which  minute  channels  {canaliculi)  extend 
in  all  directions  to  unite  with  canaliculi  from  adjoining  spaces  (Fig. 
31).  Delicate  cell  processes  extend  into  the  canaliculi  and  there 
anastomose  with  processes  from  other  cells  thus  forming  a  sort  of 
syncytium   (Fig.   32).     Owing  to   the  extreme  sensitiveness  of  the 


84 


THE  TISSUES 
h 


,     /'   -/  -' 


t-7 


Fig.  29. — Areolar  Connective  Tissue  (Rauber-Kopsch). 

a,  White  fibre,     b,  Elastic  fibre,     c,  Fixed  connective  tissue  cell,     d,  Clasmocyte. 

e,  Leucocyte  (wandering  cell).    /,  Mast  cell. 


Fig.  30. — Fibrillar  Connective  Tissue  (Areolar  Type)  from  Subcutaneous  Tissue  of 
Rabbit  (technic  2,  p.  96).  X500.  a,  Fixed  connective-tissue  cell;  b,  fibrillated  fibres; 
c  elastic  fibre  with  curled  broken  end;  d,  elastic  fibres  showing  Y-shaped  branching. 


THE  CONNECTIVE  TISSUES  85 

protoplasm  of  the  connective-tissue  cell  to  most  fixatives,  its  usual 
appearance  is  that  of  a  minute  amount  of  cytoplasm  shrunken 
down  around  a  nucleus.  Somewhat  similar  cells  with  more  coarsely- 
granular  or  vacuolated  cytoplasm  have  been  designated  "clas- 
mocytes"  (Ranvier).  By  some  these  are  believed  to  be  of  leucocyte- 
origin,  by  others  to  be  an  earlier  stage  in  the  development  of  the 
fixed  connective-tissue  cell. 

{h)  Plasma  Cells. — These  cells  occur  mainly  near  the  smaller 
blood-vessels.     Their  protoplasm  is  finely  granular  and  stains  with 


Fig.  31. — Section  ot  Human  Cornea  cut  Tangential  to  Surface.  X350.  (Technic 
9,  p.  97.)  Connective-tissue  Cell  Spaces  (Lacunae)  and  Anastomosing  Canaliculi, 
white;  whole  Intercellular  Substance  (Ground  Substance  and  Fibres),  dark. 

basic  aniline  dyes.  They  frequently  contain  vacuoles.  Their 
nuclei  are  small,  spherical  and  usually  excentric.  Small  plasma  cells 
are  about  the  size  of  leucocytes,  which  they  closely  resemble.  Large 
plasma  cells  are  larger  than  leucocytes  and  richer  in  protoplasm. 
Some  consider  them  as  derived  from  leucocytes,  others  as  a  modified 
form  of  the  ordinary  fixed  connective-tissue  cell. 

(c)  Mast  cells  are  spherical  or  irregular-shaped  cells,  found  like 
the  preceding  in  the  neighborhood  of  the  blood-vessels.  Their  proto- 
plasm contains  coarse  granules  which  stain  intensely  with  basic 
aniline  dyes  (Fig.  29).  They  are  bcHeved  by  some  investigators  to 
be  connected  with  the  formation  of  fat;  by  others  to  represent  a 
stage  in  the  development  of  the  fixed  connective-tissue  cell. 

(d)  Clasmalocyles. — These  are  large,  mostly  spindle  shaped  cells 
with  granular  protoplasm. 


ob  THE  TISSUES 

Connective-tissue  cells  may  be  pigmented  (Fig.  33).  In  such 
cells  the  cytoplasm  is  more  or  less  filled  with  brown  or  black  pigment 
granules.  In  man  pigmented  connective-tissue  cells  occur  in  the 
skin,  chorioid  and  iris. 

The  so-called  wandering  cells  (Fig.  29)  are  not  properly  a  part  of 

■i 
y  ,        _^ -1  t 

,  ,.  i  '"•'■^'  :  ■''.■■■?■-"■  ;'■ — 


Jj, 


^•f    A    /  T  ,    //t  /  i 


,?  V  //'"■■,    \ 


\  ^'  Z:^, -Ts 


\  ^ 


\\ 


X  <      . .  / 


Fig.  32. — Section  of  Human  Cornea  cut  Tangential  to  Surface.  X350.  (Technic 
8,  p.  97.)  Connective-tissue  Cells  with  Anastomosing  Processes,  stained;  Intercellular 
Substance.     (Ground  Substance  and  Fibres),  unstained. 


connective  tissue,  being  merely  amoeboid  white  blood  cells  (see  page 
107)  which  have  passed  out  from  the  vessel  into  the  tissues.  They  are 
not  pecuHar  to  connective  tissue,  being  found  in  other  tissues,  e.g., 
in  epithelium. 

The  Intercellular  Substance. — (a)  Fibres.     White  or  fihrillated 
•?«•'■:••!••:-  -  —        fibres  are  bundles   of   ex- 

tremely fine  fibrillae  (o .  5// 
in  diameter)  (Fig.  30). 
The  fibrillae  He  parallel  to 
one  another  and  are  united 
by  a  small  amount  of 
cement  substance.  The 
fibrillae  do  not  branch. 
The  fibre  bundles,  on  the 
other  hand,  branch 
dichotomously  and  anas- 
tomose.    White  fibres,  on  boihng,  yield  gelatin. 

Yellow  or  elastic  fibres  are  apparently  homogeneous,  highly  re- 
fractive fibres,  varying  in  diameter  from  i  to  10//  (Fig.  30).  They 
branch  and  anastomose,  forming  networks.     The  smaller  fibres  are 


''■'SS^>*'rI- 


Fig.  2)3- — Pigmented  Connective-tissue  Cells 
from  Chorioid  Coat  of  Human  Eye.  X350. 
(Technic  7,  p.  97.) 


THE  CONNECTIVE  TISSUES  87 

round  on  cross  section,  the  larger  flattened  or  hexagonal  (Figs.  43 
and  44) .  Their  elasticity  is  easily  demonstrated  in  teased  specimens 
by  curKng  of  the  broken  ends  of  the  fibres  (Fig.  30).  On  boiling 
they  }ield  elastin.  Although,  when  subjected  to  the  usual  technic, 
elastic  fibres  appear  homogeneous,  they  are  probably  composed  of  a 
thin  sheath  or  membrane,  enclosing  the  more  granular  elastin.  The 
latter  stains  intensely  with  magenta,  the  sheath  remaining  unstained. 

In  addition  to  the  white  fibres  and  elastic  fibres  above  described, 
so-called  "reticular"  fibres  are  frequently  present  in  fibrillated 
connective  tissue.     (See  p.  82.) 

{h)  Basement  or  ground  substance  occurs  in  extremely  minute 
amounts  between  the  individual  fibrillce  of  the  white  fibres,  where  it 
acts  as  a  cement  substance.  The  same  material  also  forms  the 
basement  or  ground  substance  in  which  the  connective- tissue  cells 
and  fibres  He  (Fig.  31).  Difliculty  in  seeing  this  ground  substance 
is  due  to  its  transparency.  It  may  be  demonstrated  by  staining 
with  silver  nitrate.     (See  technic  9,  p.  97.) 

Much  variation  exists  in  regard  to  the  proportions  of  the  different 
elements.  This  gives  rise  to  variations  in  the  physical  characteristics 
of  the  tissue.  When  fibres  predominate  over  cells  and  ground  sub- 
stance, the  tissue  is  dense  and  hard  and  is  known  as  dense  fibrous  tissue. 
The  terms  fine  connective  tissue  and  coarse  connective  tissue  desig- 
nate the  character  of  the  fibres.  When  many  cells  are  present,  the 
tissue  is  softer  and  is  known  as  cellular  connective  tissue. 

According  to  the  arrangement  of  the  white  fibres,  fibrous  connec- 
tive tissue  is  subdivided  into  areola  or  loose  connective  tissue  and 
formed  connective  tissue. 

Areolar  or  Loose  Connective  Tissue 

In  this  the  fibres  are  irregular,  running  in  all  directions  and  in- 
terlacing, leaving  between  them  meshes  or  areolce  (Fig.  30). 

Subcutaneous  connective  tissue  is  a  typical  example  of  areolar 
tissue.  Both  white  and  elastic  fibres  are  present,  although  the  former 
predominate.  Areolar  tissue  varies  greatly  as  regards  the  relative 
number  of  cells  and  fibres  and  the  closeness  with  which  the  different 
elements  are  packed.     It  thus  varies  greatly  in  density. 

Fat  Tissue. — Adipose  tissue  or  fat  tissue  is  a  form  of  areolar 
tissue  in  which  some  of  the  cells  have  become  changed  into  fat  cells. 
Fat  tissue  is  peculiar  among  the  connective  tissues  in  that  the  cells  and 
not  the  intercellular  substance  make  up  the  bulk  and  determine  the 


THE  TISSUES 


character  of  the  tissue.  The  adult  fat  cell  is  surrounded  by  a  distinct 
cell  membrane,  and  almost  the  entire  cell  is  occupied  by  a  single 
droplet  of  fat  (Figs.  35  and  36).  The  nucleus,  flattened  and  sur- 
rounded by  a  small  amount  of  cytoplasm,  is  usually  found  pressed 
against  the  cell  wall  (Fig.  36).  This  appearance  of  a  distinct  cell 
membrane  enclosing  the  spherical  fat  droplet,  with  the  nucleus  and 
cytoplasm  pressed  into  a  cresent-shaped  mass  at  one  side,  has  given 
rise  to  the  term  "signet-ring  cell."      Fat  cells  which  occur  singly, 


Fig.  34. — Fat  Tissue  from  Human  Subcutaneous  Tissue  (Child)  to  show  Lobulation. 

X25.     (Technic  i,  p.  95.) 

or  in  small  groups,  or  in  the  developing  fat  of  young  animals  are 
spherical  (Fig.  35).  In  large  masses  of  adult  fat,  the  closely  packed 
cells  are  subjected  to  pressure  and  are  polyhedral  (Fig.  36).  Fat 
cells  are  usually  arranged  in  groups  or  lobules,  each  lobule  being 
separated  from  its  neighbors  by  fibrillar  connective  tissue  (Fig.  34). 
The  appearance  which  adult  fat  presents  can  be  understood  only 
by  reference  to  its  histogenesis.  Fat  cells  are  developed  directly 
from  embryonic  connective-tissue  cells.  In  the  human  embryo 
they  are  first  distinguishable  as  fat  cells  about  the  thirteenth  week. 
The  connective-tissue  cells  which  are  to  become  fat  cells  gather  in 
groups  in  the  meshes  of  the  capillary  network  which  marks  the  ending 
of  a  small  artery.  Each  group  is  destined  to  become  an  adult  fat  lobule 
(Fig.  37)- 


THE  CONNECTIVE  TISSUES 
a  b 


89 


Fig.  35- — Young  Fat  from  Human  Subcutaneous  Tissue.  (Child.)  X175.  (Technic 
I,  p.  95.)  a,  Interlobular  connective  tissue;  b,  fixed  connective-tissue  cell;  c,_fat  cells; 
d,  artery;  e,  nucleus  of  fat  cell  and  remains  of  cytoplasm  ("signet  ring")- 


Fig.  36. — Adult  Fat  Tissue  from  Human  Subcutaneous  Tissue.  Xi75-  (Technic 
r,  p.  95.;  a,  Fat  cells;  b,  intcrloljular  connective  tissue;  c,  nucleus  of  fat  cell  and  remains 
of  cytoplasm  f" signet  ring");  d,  artery. 


90 


THE  TISSUES 


Fat  first  appears  as  minute  droplets  in  the  cytoplasm  of  the  em- 
bryonic connective- tissue  cell  (Fig.  38).     These  small  droplets  in- 


Fig.  37. — Developing  Fat  Tissue  from  Subcutaneous  Tissue  of  Five-inch  Foetal 
Pig.  X75.  (Technic  2,  p.  96.)  a,  Arteriole  breaking  up  into  capillary  network;  h, 
embryonal  connective  tissue;  c,  embryonal  fat  lobule  developing  around  blood-vessels. 


'*W 


Fig.  38. — Developing  Fat  Tissue  from  Subcutaneous  Tissue  of  Five-inch  Foetal 
Pig.  (Technic  2,  p.  96.)  a,  Arteriole  breaking  up  into  capillary  network;  b,  embryonal 
connective  tissue,  embryonal  cells  from  which  fat  cells  are  developing;  c,  capillaries. 
Fat  droplets  stained  black.  At  the  right  are  five  individual  cells  showing  stages  of 
development  from  an  embryonal  cell  to  an  adtdt  fat  cell. 

crease  in  number  and  finally  coalesce  to  form  a  single  larger  droplet. 
This  increases  in  size  and  ultimately  almost  wholly  replaces  the  cyto- 


THE  CONNECTIVE  TISSUES  91 

plasm.  In  this  way  the  nucleus  and  remaining  cytoplasm  are  pressed 
to  one  side  and  come  to  occupy  the  inconspicuous  position  which  they 
have  in  adult  fat. 

The  blood  supply  of  fat  is  rich  and  the  adult  lobule  maintains  its 
embryonic  vascular  relations,  in  that  the  vascular  supply  of  each 
lobule  is  complete  and  independent.  One  artery  runs  to  each  lobule, 
where  it  breaks  up  into  an  intralobular  capillary  network,  which  in 
turn  gives  rise  to  the  intralobular  veins,  usually  two  in  number. 

Fat  is  thus  seen  to  be  a  connective  tissue  in  which  some  of  the  cells 
have  undergone  specialization.  There  still  remain,  however,  embry- 
onal connective-tissue  cells  which  are  not  destined  to  become  fat 
cells,  but  which  develop  into  cells  and  fibres  of 
ordinary  fibrous  connective  tissue.  A  few  of  these 
remain  among  the  fat  cells  to  become  the  deUcate 
intralobular  connective  tissue  seen  in  adult  fat. 
The  majority  are,  however,  pushed  to  one  side  by 
the  developing  lobules,  where  they  form  the  inter- 
lobular septa. 


Fig.  39.  Fig.  40. 

Fig.  39. — Longitudinal  Section  of  Tendon  from  Frog's  Gastrocnemius.     X  250.    The 
nuclei  of  the  flattened  cells  are  seen  lying  in  rows  between  the  connective-tissue  fibres. 
Fig.  40. — Teased  tendon  fibres  with  cells  lying  on  their  surface.     X400.     (Ranvier.) 

Formed  Connective  Tissue. — In  formed  connective  tissue  the 
tissue  elements  instead  of  being  disposed  irregularly  as  in  areolar 
tissue,  are  arranged  with  some  regularity  or  order,  thus  giving  the 
tissue  more  or  less  definite  form. 

Tendons  and  ligaments  are  examples  of  formed  connective  tissue 
in  which  the  fibres  all  run  in  approximately  the  same  direction 
(Fig.  39).  Elastic  fibres  are  absent  or  present  in  very  small  numbers. 
The  predominance  of  the  white  fibres  and  their  parallel  arrange- 
ment result  in  great  strength  with  almost  no  extensibility.     While 


92 


THE  TISSUES 


the  individual  fibrils  do  not  branch,  groups  of  fibrils  pass  from  one 
bundle  to  another.  There  is  little  ground  substance  and  cells  are 
comparatively  few.  The  latter  are,  however,  so  characteristic  as 
to  have  received  the  name  of  tendon  cells  (Fig.  41).  They  are  irregu- 
larly rectangular  cells,  have  rather  more  breadth  than  length  and  are 
arranged  in  characteristic  rows  between  the  fibre  bundles.  The  cell 
margins  are  contiguous  and  the 
usually  excentric  nuclei  tend  to  lie 
in  adjacent  sides  of  two  cells,  thus 
giving  the  cells  the  appearance  of 
being  arranged  in  pairs  (Fig.  40). 
Thin  plate-like  extensions  of  the 


''^teasris*.^^  ' 


Fig.  41.  Fig.  42. 

Fig.  41. — -Tendon  Cells  from  the  Tail  of  a  Rat.  Stained  in  methylene-blue  {intra 
vitam).     (Bohm-Davidoff.) 

Fig.  42. — Pavement  Endothelium  of  Tendon  of  Rat.  A ,  intercellular  substance  im- 
pregnated with  silver  nitrate;  B,  tendon  fibres.     Xir5.     (Branca.) 

cell  (Fig.  41)  pass  into  the  ground  substance  between  the  fibre 
bundles  and  when  the  cell  is  seen  on  flat,  the  greater  thickness  of 
the  cell  through  the  extensions  gives  the  optical  effect  of  dark  lines 
in  the  cell  body. 

Aponeuroses. — In  thin  aponeurotic  tissue  the  fibres  are  disposed 
in  two  planes,  the  fibres  of  one  plane  running  approximately  at 
right  angles  to  those  of  the  other  plane.  The  cells  resemble  tendon 
cells  and  he  upon  the  fibre  bundles.  In  thicker  aponeuroses  the 
fibres  are  arranged  in  planes  but  their  disposition  is  more  irregular. 


Elastic  Tissue 

Elastic  fibres  occurring  in  fibrous  connective  tissue  have  been 
described.  When  the  elastic  fibres  predominate  the  tissue  is  known 
as  elastic  tissue.  Almost  pure  elastic  tissue  is  found  in  the  liga- 
mentum  nuchse  of  quadrupeds.  In  man  it  occurs  mainly  in  the 
ligamenta  subflava,  in  some  of  the  laryngeal  ligaments,  in  the  walls 


THE  COXXECTIVE  TISSUES 


93 


of  the  trachea  and  bronchi  and  of  arteries.  In  the  ligamentum 
nuchas  the  fibres  are  coarse  and  arranged  in  bundles  separated 
from   one   another  by  white  fibrous  tissue  containino;  connective- 


FiG.  43. — Coarse  Elastic  Fibres  from  Ligamentum  Xuchie.     Xsoo.     Teased  specimen. 

(Technic  10,  p.  97. j 

tissue  cells.  This  white  fibrous  tissue  also  penetrates  the  bundles 
and  separates  the  individual  elastic  fibres.  A  few  white  fibres 
and  connective- tissue  cells  are  also  present  (Figs.  43  and  44). 


(  .,-  h 


V>- 


Fig.  44. — Cross  Section  of  Coarse  Elastic  Fibres  from  Ligamentum  Nuchae.  Xsoo. 
CTechnic  10,  p.  97.)  a,  Elastic  fibres;  b,  white  fibrous  tissue  and  cement  substance. 
The  nuclei  arc  the  nuclei  of  fixed  connective-tissue  cells. 

Elastic  tissue  may  be  arranged  as  thin  membranes,  as  e.g.,  in  the 
walls  of  blood-vessels.  These  membranes  are  usually  described  as 
composed  of  a  dense  mass  of  flat,  ribbon-like  elastic  fibres,  which 


94 


THE  TISSUES 


interlace  in  such  a  manner  as  to  leave  openings  in  the  membrane. 
Hence  the  term  "fenestrated  membrane."  They  have  been  re- 
cently described  as  consisting  of  a  central  layer  composed  of  elastin, 
staining  with  magenta,  and  on  either  side  a  thin,  transparent  sheath 
unstained  by  magenta.  This  is  seen  to  correspond  to  Mall's  de- 
scription of  the  structure  of  the  elastic  fibre.  Only  the  middle  of 
theselayers  is  fenestrated. 

Reticular  Tissue 

Reticular   connective   tissue   is   a   form   of   fibrillar   connective 
tissue.     It  consists  of  extremely  delicate  fibrils  with  no   ground 


Fig.  45. — Reticular  Tissue  from  a  Human  Lymph  Node.  (Technic,  below.)  a, 
Reticular  connective  tissue,  in  the  meshes  of  which  are  suspended  b,  leucocytes,  and  c, 
lymphocytes.  The  reticular  connective  tissue  is  present  also  in  the  more  dense 
lymphatic  tissue  seen  in  the  lower  part  of  the  figure,  but  is  not  visible  on  account  of  the 
closely  packed  cells. 

substance.     The  fibrils  are  grouped  in  larger  or  smaller  bundles 
which  form  a  network  or  feltwork  enclosing  spaces,  thus  constitut- 


THE  CONNECTIVE  TISSUES  95 

ing  a  reticulum.  The  fibrils  present  much  the  same  microscopic 
appearance  as  the  white  fibres  of  areolar  tissue.  Also  in  certain 
organs,  e.g.,  the  lymph  nodes,  the  direct  continuity  of  the  fibres  of  the 
coarser  fibrous  tissue  of  the  trabeculaae  with  the  fibrils  of  the  reticular 
tissue  can  be  easily  demonstrated.  In  some  locations,  e.g.,  in  the 
lymph  nodes  (Fig.  45)  the  cells  of  the  reticular  tissue  lie  upon  the 
surface  of  the  fibrils  and  so  completely  invest  them  that  the  fibrillar 
character  of  the  tissue  cannot  be  seen  until  the  overlying  cells  have 
been  removed.  This  led  to  the  description  of  the  reticulum  of 
lymphatic  tissue  as  composed  wholly  of  anastomosing  cells. 

Reticular  tissue  has  been  described  as  yielding  on  boiling,  a  sub- 
stance called  by  some  elastin  by  others  reticulin  instead  of  gelatin 
which  results  from  boihng  fibrous  tissue.  Other  recent  studies 
upon  the  chemistry  of  reticular  tissue  are  not  however  in  accord 
with  this  view,  reticular  tissue  bring  found  to  yield  gelatin  on  boil- 
ing. Both  tissues  resist  pancreatic  digestion,  and  the  question  as 
to  the  structural  and  chemical  relations  of  the  two  tissues  remains 
at  present  unsettled. 

Reticular  connective  tissue  forms  the  framework  of  adenoid 
tissue  and  of  bone-marrow.  It  is  also  present  in  large  amounts  in 
the  spleen  and  in  the  mucous  membrane  of  the  gastro-intestinal 
tract,  lung,  liver,  kidney,  and  other  organs  where  it  forms  the 
finer  part  of  the  framework,  supporting  the  capillaries,  and  often 
apparently  ser\dng  as  a  basement  membrane  for  the  gland  cells. 

TECHNIC 

I.  Areolar  Tissue,  to  show  White  and  Elastic  Fibres. — Remove  a  bit  of  the 
subcutaneous  tissue,  as  free  from  fat  as  possible,  from  a  recently  killed  animal. 
Place  it  upon  a  mounting  slide  and  with  teasing  needles  quickly  spread  it  out  in 
a  thin  layer.  During  this  manipulation  the  specimen  should  be  kept  moist  by 
breathing  on  it.  Put  a  drop  of  sodium  chlorid  solution  upon  the  specimen  and 
cover. 

As  the  specimen  is  unstained,  a  small  diaphragm  should  be  used  for  the  micro- 
scopic examination. 

The  white  fibres  are  straight  or  wavy,  are  crossed  in  all  directions,  and  are 
longitudinally  striated.  The  elastic  fibres  have  been  stretched  and  show  as 
sharp  lines  with  curled  ends  where  the  fibres  are  broken. 

Place  a  drop  of  hydric  acetate,  i-per-cent.  aqueous  solution,  at  one  side  of  the 
cover  and  a  bit  of  filter  paper  at  the  other  side.  The  filter  paper  absorbs  the  salt 
solution,  which  is  replaced  by  the  hydric  acetate.  The  latter  causes  the  white 
fibres  to  swell  and  become  indistinct  while  the  elastic  fibres  show  more  plainly. 


96  THE  TISSUES 

2.  Areolar  Tissue,  to  show  Cells  and  Elastic  Fibres. — Prepare  second  speci- 
men of  areolar  tissue  in  the  same  manner  as  the  preceding.  Instead  of  mounting 
in  salt  solution,  allow  it  to  become  perfectly  dry,  then  stain  in  the  following 
solution: 

Gentian  violet,  saturated  aqueous  solution,  40  c.c. 

Water,  60  c.c. 

Wash  thoroughly,  dry,  and  mount  in  balsam. 

The  nuclei  of  the  fixed  connective-tissue  cells  are  stained  violet.  Their  deli- 
cate cell  bodies  show  as  an  irregular  haze  around  the  nuclei.  Both  nuclei  and 
cell  bodies  appear  cut  in  all  directions  by  the  stretched  elastic  fibres.  Wander- 
ing cells  (leucocytes)  may  usually  be  seen.  Plasma  cells  are  frequently  not 
demonstrable,  and  mast  cells  are  only  occasionally  present.  The  elastic  fibres 
are  stained  violet.     The  white  fibres  are  almost  unstained. 

While  these  methods  are  most  satisfactory  for  bringing  out  the  different  con- 
nective-tissue elements,  they  are  misleading  to  the  student  in  that  they  show  a 
picture  of  connective  tissue  after  special  preparation,  rather  than  as  it  usually 
appears  in  sections.  For  contrast  the  student  should  study  carefully  the  con- 
nective tissue  as  it  appears  in  sections  through  the  skin,  the  mucous  membranes 
and  other  organs. 

3.  Formed  Connective  Tissue. — ^Fibrous  tissue  arranged  in  the  form  of  a  net- 
work may  be  seen  in  the  specimen  of  omentum  (technic  7,  p.  79). 

4.  Densely  formed  connective  tissue  may  be  studied  in  tendon.  Cut  through 
the  skin  of  the  tail  of  a  recently  kiUed  mouse  about  half  an  inch  from  the  tip  and 
break  the  tail  at  this  point.  By  pulling  on  the  end  of  the  tail  this  portion  may 
now  be  separated  from  the  rest  of  the  tail,  carrying  with  it  long  delicate  tendon 
fibrils,  which  have  been  pulled  out  of  their  sheaths.  These  should  be  immedi- 
ately examined  in  salt  solution,  using  the  high  power  and  a  small  diaphragm. 
The  fibrils  are  seen  arranged  in  parallel  bundles. 

5.  Place  a  drop  of  hydric  acetate  (2-per-cent.  aqueous  solution)  at  one  side 
of  the  cover-glass,  absorbing  the  salt  solution  from  the  opposite  side  by  means 
of  filter  paper.  The  fibres  swell  and  become  almost  invisible,  while  rows  of 
connective-tissue  cells  (tendon  cells)  can  now  be  seen.  The  cells  may  be  stained 
by  allowing  a  drop  of  haematoxylin  or  of  carmine  solution  to  run  under  the  cover. 
After  the  cells  are  sufficiently  stained,  the  excess  of  stain  is  removed  by  washing, 
and  the  specimen  mounted  in  glycerin. 

6.  Fix  a  small  piece  of  any  good-sized  tendon  in  formalin-Miiller's  fluid  (page 
7).  After  a  week,  harden  in  alcohol,  embed  in  celloidin,  and  make  longitudinal 
and  transverse  sections.  Stain  strongly  with  haematoxylin,  followed  by  picro- 
acid-fuchsin  (page  20) .     Mount  in  balsam. 

7.  Pigmented  connective-tissue  cells  are  most  conveniently  obtained  from 
the  chorioid  coat  of  the  eye.  Fix  an  eye  in  formalin-Miiller's  fluid  (see  page  7), 
cut  in  half,  remove  chorioid  and  retina  and  pick  off  the  dark  shreds  which  cling 
to  the  outer  surface  of  the  chorioid  and  inner  surface  of  the  sclera.  These  may 
be  transferred  directly  to  glycerin,  in  which  they  are  mounted,  or  the  bits  of 
tissue  may  be  first  stained  with  haematoxylin  (page  17).     In  addition  to  the  pig- 


THE  CONNECTIVE  TISSUES  97 

mented  cells  should  be  noted  the  ordinary  fixed  connective-tissue  cells  which  lie 
among  them.     Only  the  nuclei  of  these  cells  can  be  seen. 

8.  Connective-tissue  cells  to  show  anastomosing  processes. — Stain  a  cornea 
with  gold  chlorid  (see  page  28).  Sections  are  made  tangential  to  the  convex 
surface  and  are  mounted  in  glycerin. 

9.  Connective-tissue  cell  spaces  (lacunae)  and  their  anastomosing  canaliculi 
may  be  demonstrated  by  staining  a  cornea  with  sUver  nitrate  (see  page  28). 
The  silver  stains  the  ground  substance  of  the  cornea,  leaving  the  lacunae  and 
canaliculi  unstained.  The  relation  which  this  picture  bears  to  the  preceding 
should  be  borne  in  mind  (see  Figs.  31  and  32). 

10.  Coarse  elastic  fibres  may  be  obtained  from  the  ligamentum  nuchas,  which 
consists  almost  whoUy  of  elastic  tissue.  A  piece  of  the  ligament  is  fixed  in  satu- 
rated aqueous  solution  of  picric  acid  and  hardened  in  alcohol.  A  bit  of  this 
tissue  is  teased  apart  on  a  glass  slide  in  a  drop  of  pure  glycerin,  in  which  it  is  also 
mounted.  Before  putting  into  glycerin,  the  specimen  may  be  stained  with  picro- 
acid-fuchsin.  This  intensifies  the  yellow  of  the  elastic  fibres  and  brings  out  in 
red  the  fibrillar  connective  tissue.  Pieces  of  the  ligament  fixed  and  hardened 
in  the  same  manner  may  be  embedded  in  celloidin  and  cut  into  longitudinal  and 
transverse  sections.  These  stained  with  picro-acid-fuchsin  show  well  the  rela- 
tion of  the  coarse  elastic  fibres  (yellow)  to  the  more  delicate  fibrous  tissues  (red). 

11.  Fat  Tissue. — Human  subcutaneous  fat  as  fresh  as  possible  is  fixed  in 
formalin-Miiller's  fluid  (technic  5,  p.  7),  hardened  in  alcohol  and  embedded  in 
ceUoidin.  Sections  are  stained  with  haematoxylin  and  picro-acid-fuchsin  (technic 
3,  p.  21).  The  alcohol  and  ether  of  the  celloidin  remove  the  fat  from  the  fat 
cells,  leaving  only  the  cell  membranes.  The  fat  gives  the  ceUoidin  a  milky 
appearance.  Such  ceUoidin  does  not  cut  weU.  The  ceUoidin  should,  there- 
fore, be  changed  untU  it  ceases  to  turn  white.  The  sections  are  cleared  in  oU  of 
origanum  or  carbol-xylol,  and  mounted  in  balsam.  The  fibriUar  tissue  is  stained 
red  by  the  fuchsin,  and  the  protoplasm  of  the  fat  ceU  yeUow  by  the  picric  acid. 

12.  Developing  Fat  Tissue. — Remove  bits  of  tissue  from  the  axUla  or  groin 
of  a  five-inch  foetal  pig,  or  other  foetus  of  about  the  same  development.  Fix 
twenty-four  hours  in  a  i-per-cent.  aqueous  solution  of  osmic  acid  (technic  10, 
p.  31),  wash  thoroughly  and  mount  in  glycerin.  A  part  of  the  tissue  mounted 
should  be  thoroughly  teased,  the  rest  gently  pulled  apart.  The  teased  portion 
wiU  show  the  fat  ceUs  in  various  stages  of  development.  The  unteased  part  wiU 
usuaUy  show  brownish  blood-vessels  and  the  grouping  of  fat  ceUs  around  them, 
to  form  embryonic  fat  lobules.  Note  the  developing  connective  tissue  between 
the  groups  of  fat  cells.  It  is  from  this  that  the  areolar  tissue,  which  envelops 
and  separates  the  lobules  of  adult  fat,  is  developed. 

13.  Reticular  Tissue. — Fix  a  lymph  node  in  formalin-MuUer's  fluid  (technic 
5,  p.  7),  and  stain  very  thin  sections  with  haematoxylin  and  picro-acid-fuchsin 
(technic  3,  p.  21).  In  the  lymph  sinuses  of  the  medulla  the  reticulum  can 
usually  be  plainly  seen. 

Cartilage 

Cartilage  is  a  form  of  connective  tissue  in  which  the  ground  sub- 
stance is  firm  and  dense  and  determines  the  physical  character  of  the 


98 


THE  TISSUES 


tissue.  On  boiling  it  yields  chondrin.  Cartilage  cells  are  differen- 
tiated connective-tissue  cells.  While  varying  greatly  in  shape  they 
are  most  frequently  spherical  or  oval.  Each  cell  lies  in  a  cell  space 
or  lacuna,  which  it  completely  fills.  The  intercellular  substance 
im.mediately  surrounding  a  lacuna  is  frequently  arranged  concentri- 
cally, forming  a  sort  of  capsule.  Fine  canaliculi  connecting  the 
lacunae  are  present  in  some  of  the  lower  animals  and  have'  been  de- 
scribed in  human  cartilage.  They  can  be  demonstrated,  however,  in 
human  cartilage,  only  by  special  methods,  and  probably  represent 
artefacts. 

Cartilage  contains  no  blood-vessels,  and  in  human  cartilage  no 
lymph  channels  have  been  positively  demonstrated. 


■^1 


of''' 


0m     4i>N 


ri9 


(0) 


•fs) 


Fig.  46. — Hyaline  Cartilage   from  Head   of   Frog's  Femur.     X350.     (Technic 
100.)     Groups  of  cartilage  cells  in  apparently  homogeneous  matrix. 


Cartilage  is  subdivided  according  to  the  character  of  its  inter- 
cellular substance  into  three  varieties:  (i)  Hyaline,  (2)  elastic,  (3) 
fibrous. 

I .  Hyaline  Cartilage  (Fig.  46) . — The  cells  occur  singly  or  in  groups 
of  two  or  multiples  of  two.  An  entire  group  of  cells  frequently  lies 
in  one  lucuna  surrounded  by  a  single  capsule.  Such  a  group  of  cells 
has  developed  within  its  capsule  from  a  single  parent  cell.  In  other 
cases  delicate  hyaline  partitions  separate  the  cells  of  a  group.  The 
cells  are  spherical  or  oval,  with  flattening  of  adjacent  sides.  The 
nucleus  is  centrally  placed,  and  has  a  distinct  intranuclear  network  and 
membrane.     The  cytoplasm  is  finely  granular,  and  may  contain  drop- 


THE  CONNECTIVE  TISSUES 


99 


lets  of  fat,  of  glycogen,  or  of  both.  Toward  the  perichondrium  the 
arrangement  of  the  cells  in  groups  is  less  distinct.  Here  the  cells  are 
fusiform  and  parallel  to  the  surface. 

The  intercellular  matrix,  when  subjected  to  the  usual  technic, 
appears  homogeneous.  By  the  use  of  special  methods,  such,  e.g.,  as 
artificial  digestion,  this  apparently  structureless  matrix  has  been 
shown  to  be  made  up  of  bundles  of  fibres,  quite  similar  to  those  found 
in  fibrous  connective  tissue. 

Hyaline  cartilage  forms  the  articular  cartilages  of  joints,  the  costal 
cartilages,  and  the  cartilages  of  the  nose,  trachea,  and  bronchi.  In 
the   embryo   a  young   type  of 


^'1^% 


4W 


Fig.  47. — Elastic  Cartilage  from  Dog's 
Ear.  X350.  (Technic  2,  p.  100.)  Groups 
of  cartilage  cells  in  fibro-elastic  matrix. 


hyaline  cartilage,  known  as  em- 
bryonal cartilage,  forms  the 
matrix  in  which  most  of  the 
bones  are  developed. 

2.  Elastic  cartilage  (Fig.  47) 
resembles  hyaline,  but  differs 
from  the  latter  in  that  its  hya- 
line matrix  contains  a  large 
number  of  elastic  fibres.  These 
vary  in  size,  many  being  ex- 
tremely fine.  The  elastic  fibres 
branch  and  run  in  all  directions, 
forming  a  dense  network  of  inter- 
lacing and  anastomosing  fibres. 

Elastic  cartilage  occurs  in  the  external  ear,  the  Eustachian  tube, 
the  epiglottis,  and  in  some  of  the  laryngeal  cartilages. 

3.  Fibrous  cartilage  (Fig.  48)  is  composed  mainly  of  fibrillar  con- 
nective tissue.  The  fibres  may  have  a  parallel  arrangement,  or  may 
run  in  all  directions.  Cells  are  few,  and  are  usually  arranged  in  rows 
of  from  two  to  six,  lying  in  elongated  cell  spaces  between  the  fibre 
bundles. 

Fibrous  cartilage  occurs  in  the  inferior  maxillary  and  sternoclavic- 
ular articulations,  in  the  symphysis  pubis,  and  in  the  intervertebral 
discs. 

Cartilage,  excej)t  where  it  forms  articular  surfaces,  is  covered  by 
a  membrane,  the  perichondrium.  This  is  composed  of  fibrillar  con- 
nective tissue,  and  blends  without  distinct  demarcation  with  the 
superficial  layers  of  the  cartilage. 

Like  the  other  connective  tissues,  cartilage  develops  from  meso- 


100 


THE  TISSUES 


derm.  It  is  at  first  wholly  cellular.  Each  cell  forms  a  capsule  around 
itself,  and  by  blending  of  these  capsules  are  formed  the  first  elements 
of  the  intercellular  matrix.  This  increases  in  quantity  and  assumes 
the  structural  characteristics  of  one  of  the  forms  of  cartilage.  The 
white  fibres  of  fibro-cartilage  and  the  yellow  fibres  of  elastic  cartilage 
develop  in  the  same  manner  as  in  fibrillar  and  elastic  tissue. 


Fig.    48. — -Fibrous  Cartilage  from  Dog's  Intervertebral  Disc.     X3S0.     (Technic3, 
p.  100.)     Groups  of  cartilage  cells  in  matrix  of  fibrillar  connective  tissue. 

TECHNIC 

(i)  Hyaline  Cartilage. — Remove  a  frog's  femur  and  immediately  immerse  the 
head  in  saturated  aqueous  solution  of  picric  acid.  Cut  sections  tangential  to  the 
rounded  head,  keeping  knife  and  bone  wet  with  the  picric  acid  solution.  As  bone 
must  be  cut,  a  special  razor  kept  for  the  purpose  should  be  used.  Cut  sections  as 
thin  as  possible.  The  first  sections  consist  whoUy  of  cartilage.  As  bone  is 
reached,  the  cartilage  is  confined  to  a  ring  around  the  bone.  Mount  in  the 
picric-acid  solution,  cementing  the  cover-glass  immediately. 

(2)  Elastic  Cartilage. — Remove  a  piece  of  cartUage  from  the  ear  and  fiji  in 
formalin-Miiller's  fluid  (technic  5,  p.  7).  Stain  sections  strongly  with  haema- 
toxylin,  followed  by  picro-acid-fuchsin  (technic  3,  p.  21).  Clear  in  carbol-xylol 
and  mount  in  balsam.  The  capsules  around  the  cartilage  cells  are  thick  and,  as 
they  usually  retain  some  hsematoxylin,  can  be  readily  seen.  Note  also  the 
flattened  cartilage  cells  near  the  surface,  and  the  perichondrium. 

(3)  Fibro-cartilage. — Fix  pieces  of  an  intervertebral  disc  in  formalin-Miiller's 
fluid.  Sections  are  stained  either  with  hasmatoxylin-eosin  or  with  hsematoxy- 
lin-picro-acid-fuchsin  and  mounted  in  balsam. 

Bone  tissue 

Bone  is  a  form  of  connective  tissue  in  which  the  matrix  is  ren- 
dered hard  by  the  deposition  in  it  of  inorganic  matter,  chiefly  the 


THE  CONNECTIVE  TISSUES 


101 


Fig.  49.— Bone  Tissue  showing  Lacunae  and 
Canaliculi.     X700.     (Technic  i,  p.  102.) 


of    cells    and    intercellular 


phosphate  and  the  carbonate  of  calcium.  These  salts  are  not  merely 
deposited  in  the  matrix,  but  are  intimately  associated  and  coinbined 
with  its  histological  structure.  The  intimacy  of  this  association  of 
the  organic  and  inorganic  constituents  of  bone  is  shown  by  the  fact 
that,  though  the  salts  com- 
pose two-thirds  of  bone  by 
weight,  it  is  impossible  to 
distinguish  them  by  the 
highest  magnification.  Fur- 
thermore, if  either  the  lime 
salts  are  dissolved  out  by 
means  of  acids  (decalcifica- 
tion) or  the  organic  matter 
removed  by  heating  (calcina- 
tion), the  histological  struc- 
ture of  the  bone  still  remains. 
Like  the  other  connective 
tissues,  bone  consists  morphologically 
suhstance. 

Bone  cells  or  hone  corpuscles  lie  in  distinct  cell  spaces  or  lacuncB. 
From  the  lacunae  pass  off  in  all  directions  minute  canals — canaliculi — ■ 
which  anastomose  with  canaliculi  of  neighboring  lacunae  (Fig.  49). 
At  the  surface  of  bone  these  canaliculi  open  into  the  periosteal  lymph- 
atics. A  complete  system  of  canals  is  thus 
formed,  which  traverse  the  bone  and  serve 
for  the  passage  of  nutritive  fluids.  The  bone 
cells  themselves  (Fig.  50)  are  flat,  ovoid, 
nucleated  cells,  with  numerous  fine  processes, 
which  extend  in  all  directions  into  the  can- 
aliculi. In  young  developing  bones  the 
processes  of  adjacent  cells  anastomose.  In 
adult  bone  the  processes  extend  but  a  short 
allowing  the  outline  of  the    distance  into  the  canaliculi,  and  probably  do 

lacuna  to  be  seen. 

not  anastomose. 
The  basement  substance  or  matrix  has  a  fibrous  structure, 
closely  resembling  that  of  fibrillar  connective  tissue,  and  it  is  in  this 
fibrillar  matrix  that  the  lime  salts  are  deposited.  The  fibrils  are 
held  together  by  cement  substance  into  bundles.  In  most  bone  the 
bundles  are  fine  and  arranged  in  layers  or  lamellcc.  Less  commonly 
the  fibre  bundles  are  coarser  and  have  an  irregular  arrangement. 


Fig.  50. — Bone  Cell  and 
Lacuna.  (Joseph.)  At  a 
the  cell  body  has  shrunken. 


102  THE  TISSUES 


TECHNIC 


(i)  For  the  study  of  the  minute  structure  of  bone  a  section  of  undecalcified  or 
hard  bone  is  required.  Part  of  the  shaft  of  one  of  the  long  bones  is  soaked  for  sev- 
eral days  in  water  and  all  the  soft  parts  are  removed.  It  is  then  placed  in  equal 
parts  alcohol  and  ether  to  remove  all  traces  of  fat  and  thoroughly  dried  (the 
handle  of  a  tooth  or  nail  brush  frequently  furnishes  good  material  and  is  already 
dried).  Thin  longitudinal  and  transverse  sections  are  now  cut  out  with  a  bone 
saw.  One  surface  is  next  ground  smooth,  first  on  a  glass  plate,  using  emerj^  and 
water,  then  on  a  hone.  The  specimen  is  now  fastened  polished  side  down  on  a 
block  of  wood  or  glass  by  means  of  sealing  wax,  and  the  other  side  polished 
smooth  in  the  same  manner  as  the  first,  the  bone  being  ground  as  thin  as  possible. 
The  sealing  wax  is  removed  by  soaking  in  alcohol  and  the  specimen  looked  at 
with  the  low  power.  If  not  thin  enough,  it  is  gently  rubbed  on  a  fine  hone.  It 
is  then  soaked  in  equal  parts  alcohol  and  ether,  dried  thoroughly,  and  mounted 
in  hard  balsam.  This  is  accomplished  by  placing  a  small  bit  of  hard  balsam  on 
a  slide,  melting,  pushing  a  bit  of  the  bone  into  the  hot  balsam,  covering  and 
cooling  as  quickly  as  possible.  The  object  of  the  hard  balsam  and  quick  cooling 
is  to  prevent  the  balsam  running  into  the  lacunae  and  canaliculi  and  obscuring 
them  by  its  transparency.  The  air  imprisoned  in  the  lacuna  and  canaliculi 
causes  them  to  appear  black  when  viewed  by  reflected  light. 

(2)  The  structure  of  the  bone  cell  is  best  studied  in  sections  of  decalcified 
bone  which  has  first  been  carefully  fixed.     (See  technic  i,  p.  196.) 


t  * 


•  •   • 


CHAPTER  IV 
THE  BLOOD 

Blood  is  best  considered  as  a  tissue,  the  intercellular  substance 
of  which  is  fluid.  This  fluidity  of  the  intercellular  substance  allows 
the  formed  elements  or  cells  to  move  about  freely,  so  that  there  is  not 
the  same  definite  and  fixed  relation  between  cells  and  intercellular 
substance  as  in  other  tissues.  There  are  about  5  litres  of  blood  in  the 
adult  body,  blood  thus  constituting  about  ^-  .^^^ 
one-thirteenth  of  the  entire  body  weight. 

The  fluid  intercellular  substance  or 
plasma  is  slightly  alkaline  in  reaction.  It 
consists  of  serum  albumen,  globulin, 
fibrinogen  and  inorganic  salts,  chiefly  the 
chlorid,  carbonate,  bicarbonate  and  phos- 
phate of  soda.  The  reaction  of  blood  is 
distinctly  alkahne,  due  mainly  to  the 
phosphate  of  soda.  Its  specific  gravity  is 
about  1.030,  while  that  of  the  whole  blood 
is  about  1.060.  The  bulk  of  the  plasma  is 
about  equal  to  that  of  the  red  and  the 
white  cells. 

The  formed  elements  of  the  blood  are : 
(i)  Red  blood  cells  (red  blood  corpuscles, 
erythrocytes);  (2)  white  blood  cells  (color- 
less corpuscles — leucocytes) ;  (3)  blood 
platelets  (thrombocytes);  (4)  blood  dust 
(ha^matokoniaj. 

I.  Red  blood  cells  (erythrocytes)  (Fig.  51,  i,  2,  3)  are  in  man 
non-nucleated  circular  discs.  ^  Their  average  diameter  is  about 
7.5/<,  their  thickness  2//  at  the  thin  centre.  A  few  red  blood  cells 
of  a  diameter  of  8,«  to8.5/t  (macrocytes)  and  about  the  same  number 
of  red  ceils  only  about  one-half  the  usual  diameter   (microcytes) 

'  Some  observers  describe  the  red  blood  cell  as  bell-  or  cu|)-shiii)ed.  (Lewis:  Jour. 
Med.  Research,  N.  S.,  vol.  v,  1904;  Radasch:  Anal.  Anz.  xxviii,  igc6.  Weidcnreich: 
Krgcbn.  d.  Anat.,  1903,  1904,  1909;  Arch.  f.  mikr.  Anal.,  Ixi,  1903,  Ixix,  igof).) 

103 


'  8 

Fig.  51. — Cells  from  Human 
Blood.  X  600.  (Technic  2, 
p.  no.)  I,  Red  blood  cell 
seen  on  flat;  2,red  blood  cell 
seen  on  edge;  3,  red  blood  cells 
forming  rouleaux;  4,  4,  small 
and  large  lymphocytes;  5, 
mononuclear  leucocyte;  6, 
transitional  leucocyte;  7, 
polymorphonuclear  leucocyte, 
containing  ncutrophile  gran- 
ules; 8,  polynuclear  leucocyte, 
containing  eosinophile  gran- 
ules; 9,  mononuclear  leuco- 
cyte, containing  basophile 
granules. 


104  THE  TISSUES 

are^usually  present.  They  are  biconcave,  with  rounded  edges. 
Seen  on  the  flat,  the  difference  in  thickness  between  centre  and  pe- 
riphery is  evidenced  by  the  difference  in  refraction  (Fig.  51,  i).  Seen 
on  edge,  the  shape  resembles  that  of  a  dumb-bell  (Fig.  51,  2).  Singly 
or  in  small  numbers,  red  blood  cells  have  a  pale  straw  color,  due  to 
the  presence  of  haemoglobin.  Redness  is  apparent  only  when  the 
cells  are  seen  in  large  numbers.  If  fresh  blood  be  allowed  to  stand 
for  a  moment,  the  red  cells  are  seen  to  adhere  to  one  another  by  their 
flat  surfaces,  forming  rows  or  rouleaux  (Fig.  51,  3). 

Subjected  to  the  usual  technic,  the  red  blood  cell  appears  homo- 
geneous. By  the  use  of  special  methods,  this  apparently  homogene- 
ous substance  can  be  separated  into  {a)  a  color-bearing  proteid — 
hcemoglobin,  and  (b)  a  stroma,  the  latter  representing  the  protoplasm 
of  the  cell.  Peripherally  the  stroma  probably  forms  an  extremely 
delicate  cell  membrane,  although  the  presence  of  any  membrane 
whatever  is  denied  by  some.  It  is  the  haemoglobin  which  gives  color 
to  the  corpuscles.  Haemoglobin  is  a  complex  proteid,  which  can  be 
resolved  into  a  globulin  and  a  pigment,  hcematin.  It  is  held  in  solu- 
tion or  in  suspension  in  the  stroma. 

The  red  blood  cells  are  soft  and  elastic,  and  are  easily  twisted 
to  accommodate  themselves  to  the  smallest  capillaries. 

The  red  blood  cell  is  extremely  susceptible  to  changes  in  the  plasma. 
Thus  even  slight  evaporation  of  the  plasma  results  in  osmosis  between 
the  now  denser  surrounding  fluid  and  the  contents  of  the  cell.  This 
causes  fluid  to  leave  the  cell,  with  the  result  that  the  latter  becomes 
spheroidal  and  irregularly  shrunken,  with  minute  knob-like  projec- 
tions from  its  surface.  This  is  known  as  crenation  of  the  red  cell. 
The  addition  of  water  to  blood,  thus  decreasing  the  specific  gravity 
of  the  plasma,  has  the  opposite  effect,  resulting  in  swelling  of  the  cell. 
It  also  causes  solution  of  the  haemoglobin,  which  leaves  the  cell,  the 
latter  then  appearing  colorless,  with  a  faint  circular  outline — the 
membrane  of  the  cell.  This  separation  of  the  haemoglobin  from  the 
corpuscle  is  also  caused  by  freezing  and  thawing,  by  heat  (6o°C.),  by 
the  addition  of  dilute  acids,  ether,  or  chloroform. 

Dilute  alkaline  solutions  and  bile  first  cause  the  red  corpuscles  to 
swell  and^becom.e  spherical,  and  then  to  dissolve.  This  is  known 
as  hcBfnolysis,  and  may  also  be  effected  by  mixing  the  blood  of  one 
species  with  that  of  another.  Dilute  acetic  acid  causes  swelling  and 
fading  of  the  red  cells,  with  the  form.ation  of  prism.atic  crystals  of 
hsemoglobin. 


THE  BLOOD  105 

The  red  blood  cells  number  from  4,500,000  to  5,000,000  per  cubic 
milKmeter  of  blood. 

2.  White  blood  cells  (leucocytes)  (Fig.  51,  4  to  9  inclusive)  are 
colorless  nucleated  structures  which  have  a  generally  spherical  shape, 
but  which  are  able  to  change  their  shape  on  account  of  their  powers 
of  amoeboid  movement.  They  have  a  diameter  of  from  5  to  10/^, 
and  are  much  less  numerous  than  the  red  cells,  the  proportion  being 
about  one  white  cell  to  five  hundred  red  cells,  or  about  10,000  to  the 
cubic  milHmeter.  This  proportion  is,  however,  subject  to  wide 
variation. 

Leucocytes  may  be  classified  as  follows:  (a)  Lymphocytes;  (b) 
mononuclear  leucocytes;  (c)  transitional  leucocytes;  (d)  polymor- 
phonuclear or  polynuclear  leucocytes. 

(a)  Lymphocytes  (Fig.  51,  4).^ — These  vary  in  diameter  from  5 
to  8,«,  and  are  sometimes  subdivided  into  small  lymphocytes  and 
large  lymphocytes.  The  nucleus  is  spherical,  stains  deeply,  and  al- 
most completely  fills  the  cell,  the  cytoplasm  being  confined  to  a 
narrow  zone  around  the  nucleus.  Lymphocytes  constitute  about 
20-per-cent.  of  the  white  blood  cells. 

(b)  Mononuclear  leucocytes  (Fig.  51,  5  and  9)  are  of  about 
the  same  size  as  large  lymphocytes.  The  nucleus,  however,  stains 
more  faintly  and  is  smaller,  while  the  cytoplasm  is  greater  in  amount. 
From  2-per-cent.  to  4-per-cent.  of  the  white  cells  are  mononuclear 
leucocytes. 

(c)  Transitional  leucocytes  (Fig.  51,  6)  occur  in  about  the 
same  numbers  as  the  preceding,  and  are  of  about  the  same  size.. 
There  is  relatively  more  cytoplasm,  and  the  nucleus,  instead  of 
being  spherical,  is  crescentic  or  horseshoe  or  irregular  in  shape. 
These  cells  represent  a  transitional  stage  between  the  mononuclear 
and  the  polymorphonuclear  and  polynuclear  varieties. 

(d)  Polymorphonuclear  and  polynuclear  leucocytes  (Fig. 
51,7,8)  constitute  about  70-per-cent.  of  the  white  blood  cells.  Their 
size  is  about  the  same  as  that  of  the  mononuclear  form,  but  they  are 
somewhat  more  irregular  in  shape.  The  appearance  of  the  nucleus 
is  characteristic.  In  the  polymorphonuclear  form  the  nucleus  con- 
sists of  several  round,  oval,  or  irregular  nuclear  masses  connected 
with  one  another  by  cords  of  nuclear  substance.  These  cords  are 
frequently  so  delicate  as  to  be  distinguished  with  difficulty.  The 
polynuclear  form  is  derived  from  the  polymorphonuclear  by  breaking 


106  THE  TISSUES 

down  of  the  connecting  cords,  leaving  several  separate  nuclei  or 
nuclear  segments. 

Granules  in  small  numbers  may  be  present  in  the  protoplasm  of 
any  of  the  leucocytes,  but  the  protoplasm  of  about  70  per  cent,  of  all 
leucocytes  is  so  distinctly  and  regularly  granular  that  by  some  authors 
a  prim.ary  division  into  granular  leucocytes  and  non-granular  leuco- 
cytes is  made.  Under  this  classification,  lymphocytes  and  some 
mononuclear  leucocytes  are  placed  in  the  non-granular  group,  while 
transitional  leucocytes,  polym.orphonuclear  leucocytes  and  some 
mononuclear  leucocytes,  are  placed  in  the  granular  group.  Aniline 
dyes  may  be  divided  into  acid,  basic  and  neutral,  according  to 
whether  the  coloring  matter  is  an  acid,  a  base,  or  a  combination  of  an 
acid  and  a  base,  and  the  granules  of  the  granular  leucocytes  react 
in  a  definite  manner  to  these  dyes,  thus  allowing  the  following 
classification : 

f  I  neutrophile. 
Granular  leucocytes]  2  acidophile  (eosinophile). 
[  3  basophile. 

As  the  neutrophile  granules  are  fine  and  the  eosinophile  granules 
coarse,  a  classification  of  leucocytes  into  finely  granular  and  coarsely 
granular  is  sometimes  made. ' 

1.  Neutrophile  Leucocytes. — These  are  the  most  numerous  of  all 
leucocytes,  making  up  about  68  per  cent.  Their  protoplasm  is 
thickly  studded  with  very  fine  granules  which  stain  violet  with  a 
mixture'of  eosin  (acid)  and  toluidin  blue  (basic).  Most  neutrophiles 
are  polymorphonuclear,  a  few  are  transitional.  They  have  a  wide 
distribution,  being  found  not  only  in  the  blood  itself,  but  in  the 
spleen  and  lymph  nodes  and  as  wandering  cells  in  various  tissues  and 
organs. 

2.  Acidophile  Leucocytesl  or,  because  the  most  common  acid  dye 
used  is  eosin,  eosinophile.  The  granules  in  these  cells  are  coarse 
and  sharply  defined.  They  stain  strongly  with  acid  dyes.  Eosino- 
philes  are  mainly  polymorphonuclear,  m.ore  rarely  they  are  transi- 
tional. They  make  up  from  i  per  cent,  to  4  per  cent,  of  all  leuco- 
cytes. In  certain  pathological  conditions  their  number  is  greatly 
increased. 

3.  Basophile  Leucocytes. — The  granules  in  these  cells  are  rather 
coarse  and  irregular  in  shape  and  are  distributed  unevenly  through 
the  cytoplasm.     They  stain  strongly  with  basic  dyes.     They  are 


THE  BLOOD  107 

present  in  small  numbers  (Ehrlich,  0.2  per  cent,  to  0.5  per  cent.)  in 
normal  blood,  or  they  may  not  be  demonstrable.  Ehrlich  identifies 
them  with  the  "mast  cells"  which  are  found  in  various  tissues  and 
organs,  especially  in  areolar  connective  tissue,  but  this  identity  has 
been  questioned. 

Upon    the    basis    of    the    foregoing    description    the   following 
classification  of  leucocytes  on  the  basis  of  granulation  may  be  made. 


1^  Lymphocytes  22-25   per  cent, 
f  Xon-granular  i 
I  I  Mononuclear  leucocytes  r-4  per  cent. 


Leucocytes  \ 


Neutrophile   65-72   per  cent,     (mainly  polymorphonuclear,    few 
transitional  and  mononuclear) 
Granular  \  Acidophile  1-4  per  cent,  (mainly  polymoiphonuclear,  few  transi- 

I        tional  and  mononuclear) 
[  Basophile  0.2-o.s  per  cent,  (mononuclear  and  transitional) 

The  function  of  the  red  cells  is  primarily  the  carrying  of  oxygen 
from  the  lungs  to  the  tissues  and  of  carbonic  acid  from  the  tissues 
to  the  lungs.  This  oxygen-carrying  ability  is  dependent  upon  the 
haemoglobin  and  is  directly  proportionate  to  the  number  of  red  cells 
and  to  the  richness  of  the  individual  cells  in  haemoglobin.  In  the 
capillaries  of  the  tissues  and  again  in  the  capillaries  of  the  lung  the 
haemoglobin  is  undergoing  constant  change.  The  haemoglobin  of 
arterial  blood  is  known  as  oxy haemoglobin,  of  venous  blood  as  re- 
duced haemoglobin.  The  difference  is  readily  demonstrable  by  the 
spectroscope.^ 

That  leucocytes  possess  in  a  marked  degree  the  power  of  amoe- 
boid movement  has  been  noted  (p.  52).  On  account  of  this  motility 
leucocytes  are  able  (i)  to  leave  the  blood-vessels  (diapedesis)  and 
move  about  freely  in  the  tissues  (wandering  cells),  (2)  to  surround 
and  take  up  substances  from  without  (phagocytosis). 

Diapedesis. — This  power  is  directly  dependent  upon  motility 
and  while  possessed  by  all  leucocytes  is  most  markedly  character- 
istic of  the  polymorphonuclear  forms.  (For  details  of  amoeboid 
movement  see  p.  52.) 

Phagocytosis. — Phagocytic  powers  are  not  possessed  equally 
In'  all  leucocytes,  but  are  confined  largely  to  the  mononuclear 
and  polymorphonuclear  forms.  Such  cells  can  take  up  foreign  sub- 
stances, bacteria,  degeneration  products,  etc.,  carry  them  to  other 

'Of  interest  in  this  connection  is  the  fact  that  in  poisoninjf  by  illuminating  j^as,  a 
very  definite  and  staljle  combination  of  the  carbon  rlioxid  with  the  hx-moglobin  is 
ffirmcrl  (( arboxyha.-moj^l(;binj.  It  is  this  substance  which  determines  the  darker  red 
color  ol  the  blood  in  this  condition  and  is  aijparenlly  the  cause  of  death. 


108  THE  TISSUES 

parts  of  the  body  or  entirely  outside  the  body  (salivary  corpuscles), 
or  apparently  absorb  or  digest  them.     (See  also  p.  50.)^ 

3.  Blood  platelets  (thrombocytes)  are  minute  round  or  oval 
bodies  from  2/^  to  4/^  in  diameter.  They  are  colorless  and  vary  in 
shape.  In  fixed  preparations  they  often  appear  stellate.  Their  num- 
ber has  been  variously  estimated.  The  average  is  probably  about 
200,000  to  300,000  per  cubic  millimeter  of  blood.  In  the  blood 
stream  they  are  separate,  but  show  a  marked  tendency  to  aggluti- 
nation directly  the  blood  is  drawn.  Some  comparatively  recent 
observations  tend  toward  considering  the  platelets  as  true  cells. 
Thus  they  have  been  described  as  amoeboid,  as  having  the  same 
chemical  composition  as  cells,  and  as  containing  either  granules 
of  chromatin  or  distinct  nuclear  structures.  The  so-called  throm- 
bocytes of  Ovipara  are  larger  than  those  of  man  and  are  unques- 
tionably nucleated  cells.  Their  appearance  is,  however,  wholly  un- 
like human  thrombocytes  and  the  identity  of  the  two  forms  is 
doubtful. 

Various  functions  have  been  ascribed  to  the  thrombocytes.  It 
is  fairly  established  that  they  have  something  to  do  with  the  for- 
mation of  fibrin  and  the  coagulation  of  blood. 

4.  The  blood  dust  (haematokonia)  occurs  in  the  form  of  small 
refractive  granules. 

In  the  blood  of  the  lower  mammals  and  in  herbivorous  animals 
small  droplets  of  fat  derived  from  the  chyle  are  found.  They  are 
known  as  elementary  granules  and  are  not  present  in  normal  human 
blood. 

Development  or  the  Blood. 

At  an  early  stage  of  embryonic  development  certain  mesodermic  cells  of  the 
area  vasculosa,  which  surrounds  the  embryo,  become  arranged  in  groups  known 
as  Uood  islands.  It  is  from  these  "islands"  that  both  blood  and  blood-vessels 
develop.  The  peripheral  cells  arrange  themselves  as  the  primitive  vessel  walls, 
within  which  the  central  cells  soon  become  free  as  the  first  Uood  corpuscles.  In 
this  way  vascular  channels  are  formed,  inside  of  which  are  developing  blood 
cells.  This  division  of  the  mesoblastic  cells  of  the  blood  islands  into  (i)  endothe- 
lial cells  of  the  vessel  walls  and  (2)  progenitors  of  the  blood  cells  or  primitive 
blood  ceUs,  is  quite  generally  accepted.     From  this  point,  however,  opinions 

1  It  is  to  be  noted  that  phagocytosis  is  not  confined  to  leucocytes  but  has  been  ob- 
served in  other  cells,  e.g.,  fixed  connective-tissue  cells  including  endothelium.  It  is 
also  to  be  noted  that  phagocytic  cells  are  not  equally  phagocytic  to  all  substances.  _  In 
other  words  phagocytes  apparently  have  some  powers  of  selection.  Thus  if  two  kinds 
of  bacteria  be  presented  to  them,  they  may  take  up  only  one  kind,  or  one  kind  much 
more  readily  than  the  other. 


THE  BLOOD  109 

diverge,  the  two  main  theories  of  blood-cell  formation  being  known  as  the  poly- 
phyletic  and  the  monophyletic  theories. 

According  to  the  polyphyletic  theory,  after  the  original  division  of  the  meso- 
blast  cells  of  the  blood  islands  into  vessel  wall  cells  (endothelium)  and  blood 
cells  (primary  blood  cells),  the  latter  go  on  to  the  development  of  erythroblasts 
and  these  to  the  development  of  erythrocytes.  Leucocytes  develop  later  in  con- 
nective tissue,  in  the  liver,  spleen  and  bone  marrow,  while  lymphocytes  have 
their  origin  in  the  germ  centers  of  the  lymphoid  organs.  There  are  thus  three 
separate  sources  of  blood  cells:  (i)  Red  blood  cells,  originally  from  erythroblasts 
of  the  blood  islands;  in  adult  life  from  the  erythroblasts  of  the  bone  marrow  and 
possibly  of  spleen;  (2)  leucocytes,  first  in  connective  tissue,  liver,  spleen  and  mar- 
row; in  adult  hfe  in  the  marrow;  (3)  lymphocytes,  in  the  lymphoid  organs.  Ac- 
cording to  the  polyphyletic  theory  these  three  types  are  genetically  independent 
and  remain  so  throughout  life,  the  ceUs  of  each  type  undergoing  mitotic  division 
to  produce  new  cells  of  the  same  type  only. 

According  to  the  monophyletic  theory  the  blood-cell-forming  elements  of  the 
blood  islands  fall  into  two  groups  as  regards  their  future  development:  (i)  cells 
which  give  rise  to  primary  erythroblasts,  these  to  secondary  erythroblasts  and 
these  again  to  erythrocytes,  thus  completing  the  line  of  red  blood  cells,  and  (2) 
cells  which  remain  undifferentiated,  not  only  in  the  embryo  but  throughout  Ufa, 
and  retain  the  capabiUty  of  differentiating  into  erythroblasts  or  into  white  blood 
cells,  either  leucocytes  or  lymphocytes.  According  to  Weidenreich^  and  other 
supporters  of  this  theory,  red  and  white  blood  cells  stand  in  very  close  genetic 
relation.  He  claims  that  an  undifferentiated  mother  cell  exists  which  is  capable 
of  differentiating  either  in  the  direction  of  the  red  cell  or  of  the  white  cell;  that 
this  mother  cell  exists  not  only  in  the  embryo  but  throughout  life  and  is  con- 
stantly giving  birth  to  cells  which  are  to  develop  into  red  blood  cells  or  white 
blood  cells  to  replace  those  being  constantly  used  up  and  cast  off.  Morpho- 
logically the  mother  cell  is  apparently  identical  with  the  lymphocyte.  In  post- 
embryonic  life,  this  mother  cell  is  found  in  marrow  in  the  germ  center  of  lymphoid 
organs  and  possibly  in  connective  tissue.  On  the  other  hand  a  once  differentiated 
cell  remains  a  differentiated  cell,  and  while  able  to  divide  mitotically  and  thus 
give  rise  to  cells  of  its  own  kind,  it  is  never  capable  of  producing  cells  of  any  other 
kind. 

Two  views  are  held  in  regard  to  the  manner  in  which  the  embryonic  nucleated 
red  cell  gets  rid  of  its  nucleus  in  becoming  the  non-nucleated  red  cell  of  the  adult. 
According  to  one  the  nucleus  is  absorbed  within  the  cell  and  gradually  secreted; 
according  to  the  other  the  nucleus,  as  a  whole,  is  extruded. 

In  early  embryonic  life  especially  active  proliferation  of  red  cells  occurs  in 
the  blood-vessels  of  the  liver.  This  has  led  to  the  considering  of  the  liver  as  a 
blood-forming  organ.  The  liver  cells  themselves,  however,  take  no  actual 
part  in  the  formation  of  blood  cells,  the  blind  pouch-like  venous  capillaries  of 
the  liver,  with  their  slow-moving  blood  currents,  merely  furnishing  a  peculiarly 
suitable  place  for  cellular  proliferation.  Before  birth  the  splenic  pulp  and  bone 
marrow  become  blood-forming  organs.  In  the  adult  the  bone  marrow  is  prob- 
ably, under  normal  conditions,  the  main  if  not  the  sole  seat  of  red-cell  formation. 

'  Ant.  Rec,  vol.  iv.,  Sept.,  1910, 


110  THE  TISSUES 

During  foetal  life  the  number  of  nucleated  red  cells  constantly  diminishes, 
while  the  number  of  non-nucleated  red  cells  increases.  At  birth  there  are 
usually  but  few  nucleated  red  cells  in  the  general  circulation,  although  even  in 
the  adult  they  are  always  found  in  the  red  bone-marrow. 

The  origin  of  the  blood  platelets  is  not  known.  They  have  been  described 
as  originating  in  the  extruded  nuclei  of  the  red  cells,  as  disintegrating  leucocyte 
products,  as  red  cells  in  process  of  development,  as  red  cells  in  process  of  disin- 
tegration, as  albuminoid  precipitates,  as  a  specific  blood  cell.  According  to 
Wright^,  they  are  derived  from  the  megakaryocytes  of  bone  marrow  and 
other  blood-forming  organs. 

TECHNIC 

(i)  Fresh  Blood. — Prick  a  finger  with  a  sterile  needle.  Touch  the  drop  of 
blood  to  the  centre  of  the  slide  and  cover  quickly.  For  immediate  examination 
of  fresh  blood  no  further  preparation  is  necessary.  Evaporation  may  be  pre- 
vented by  cementing,  or  by  smearing  a  rim  of  vaseline  around  the  cover-glass. 

(2)  Blood  Smears. — From  the  same  or  a  second  prick  take  up  a  drop  of 
blood  along  the  edge  of  a  mounting  slide.  Quickly  place  the  edge  against  the 
surface  of  a  second  slide  and  draw  the  edge  across  the  surface  in  such  a  manner  as 
to  leave  a  thin  film  or  smear  of  blood.  AUow  the  smear  to  become  perfectly  dry 
and  stain  by  technic  1 1 ,  p.  3 1 .  By  this  method  the  acidophile  granules  are  stained 
red,  basophile  granules  purple,  and  neutrophUe  granules  a  reddish-violet. 

Good  results  may  also  be  obtained  by  fixing  the  dried  smear  for  half  an  hour 
in  equal  parts  alcohol  and  ether  and  staining  first  in  a  strong  alcoholic  solution 
of  eosin,  then  in  a  rather  weak  aqueous  solution  of  methylene  blue. 

^  Jour.  Morph.,  xxi,  1910. 


CHAPTER  V 

MUSCLE  TISSUE 

While  protoplasm  in  general  possesses  the  property  of  contrac- 
tiKty,  it  is  in  muscle  tissue  that  this  property  reaches  its  highest  de- 
velopment.    INIoreover,  in  muscle  this  contractiHty  is  along  definite 


Fig.  52.^ — Isolated  Smooth  Muscle  Cells  from  Human  Small  Intestine.  X403. 
(Technic  i,  p.  124.)  Rod-shaped  nucleus  surrounded  by  area  of  finely  granular  pro- 
toplasm; longitudinal  striations  of  cytoplasm. 

directions,  and  is  capable  of  causing  motion,  not  only  in  the  cell  itself, 
but  in  structures  outside  the  cell. 

^Muscle  may  be  classified  as:  (i)  Involuntary  smooth  muscle;  (2) 
voluntary  striated  muscle;  (3)  involuntary  striated  muscle  or  heart 
muscle. 

Involuntary  Smooth  Muscle. — This  is  the  simplest  form 
of   muscle   tissue    and  consists  of    long  spindle-shaped  cells    (Fig. 


A  B 

¥\G.  53. — .Apparent  Intercellular  Bridges  of  Smooth  Muscle.  A,  From  longitudinal 
sectionof  intestine  of  guinea-pig;  B,  from  transverse  section  of  intestine  of  rabbit.  X420. 
a,  Nerve  cell;  b,  end  of  muscle  cell.     (Stohr.) 

52)  which  are  prismatic  on  transverse  section  (Fig.  53).  The  length 
of  the  smooth  muscle  cell  varies  usually  from  30  to  200/<,  its  width 
from  3  to  8/'-,'  except  in  the  pregnant  uterus  where  the  cells  fre- 
quently attain   a  much   greater   size.     Less  commonly  the  smooth 

'  In  the  walls  of  very  small  blood-vesselH  smooth   muscle  cells  15  to  2o/(  are  found. 
(Apathy; . 

Ill 


112 


THE  TISSUES 


1\ 


m 


muscle  cell  is  flattened,  and,  in  tissues  rich  in  elastic  fibres,  e.g., 
the  media  of  some  arteries,  especially  the  aorta,  is  quite  irregular 
in  shape.     The  central  thickest  part  of  each  cell  contains  an  elliptical 

or  long  rod-shaped  nucleus.  The 
nucleus  has  a  rather  coarse  intra- 
nuclear network  and  one  or  more 
nucleoh.  In  some  cells  a  centrosome 
has  been  demonstrated.  It  lies  out- 
side and  usually  just  to  one  side  of 
the  nucleus.  The  irregular,  wavy 
and  twisted  nuclei  often  seen  are 
probably  due  to  contractions  of  the 
cytoplasm.  The  nucleus  is  sur- 
rounded by  an  area  of  finely  gran- 
ular cytoplasm,  most  abundant  at 
the  poles  of  the  nucleus  where  it 
frequently  forms  a  little  pointed  cap. 
The  rest  of  the  cytoplasm  shows 
deHcate  longitudinal  striations,  which 
probably  represent  a  longitudinal 
arrangement  of  the  spongioplasm. 
These  fibrils  are  extremely  fine,  are 
frequently  present  in  small  numbers, 
are  not  arranged  in  bundles,  are  ap- 
parently homogeneous  and  anisotro- 
pic, and  are  often  very  difficult  of 
demonstration.  The  fibrils  lie  in  a 
less  differentiated  cytoplasm.  The 
smooth  muscle  cell  has  no  such  dis- 
tinct envelop  as  the  sarcolemma  of 
striated  muscle.  The  outer  cyto- 
plasm is,  however,  modified  to  form 
a  delicate  cell  membrane  or  at  least 
a  modified  surface  layer. 

The  cells  are  united  by  a  small 
amount  of  intercellular  "cement" 
substance  which  reacts  to  silver 
nitrate.  Intercellular  "bridges" 
similar  to  those  connecting  epithelial  cells  have  been  described  (Fig. 
53) ,  but  are  regarded  by  many  observers  as  artefacts.     By  others  fine 


'\''| 


,.'-,\ 


Fig.  54. — Preparation  of  Smooth 
Muscle  Cells  to  show  Fibrillar  Struc- 
ture. From  intestine  of  Triton. 
X2300.     (Heidenhain.) 


MUSCLE  TISSUE 


113 


intercellular  fibrils  are  described  as  continuous  from  cell  to  cell,  thus 
forming  a  syncytium.  Between  and  surrounding  the  smooth  muscle 
cells  is  a  network  of    delicate    connective- tissue  fibrils    (Fig.    55). 


■Fig.  55. — ^Longitudinal  Section  of  the  Musculature  of  Cat's  Intestine  to  show 
Intercellular  Connective  Tissue.     (Bohemann.) 

These  are  not  apparent  in  sections  which  have  been  subjected  to  the 
usual  technic,  but  can  be  demonstrated  either  by  digesting  the  smooth 
muscle  cells  by  means  of  trypsin,  thus  bringing  out  the  undigestible 
collagenous  fibrils,  or  by  special  staining  methods  (p.  124). 


cf 


Fig.  56. — Elastic  Fibres  in  the  Smooth  Muscle  of  Intestine  of  Cat.     (Holmgren.) 

Smooth  muscle  cells  may  be  arranged  in  layers  of  considerable 
thickness,  the  cells  having  a  definite  direction,  as  in  the  so-called 
"musculature"  of  the  intestine  (Fig.  56).     In  such  masses  of  smooth 

8 


114  THE  TISSUES 

muscle  the  cells  are  separated  into  groups  or  bundles  by  connective 
tissue.  Smooth  muscle  cells  may  be  arranged  in  a  sort  of  network, 
the  cells  crossing  and  interlacing  in  all  directions,  as  in  the  wall  of  the 
frog's  bladder.  Again,  they  may  be  scattered  in  small  groups  or 
singly  among  connective- tissue  elements,  as  in  the  villi  of  the  small 
intestine. 


-  a 

"  c 


Fig.  57. — Smooth  Muscle  from  Longitudinal  Section  of  Cat's  Small  Intestine,  show- 
ing Portions  of  Inner  Circular  and  Outer  Longitudinal  Muscle  Coats  with  Intervening 
Connective  Tissue.  X350.  (Technic  3,  p.  124.)  a,  Transversely  cut  cells  of  inner 
circular  layer;  in  comparatively  few  has  the  plane  of  section  passed  through  the  nucleus; 
b,  longitudinally  cut  cells  of  outer  longitudinal  layer.  In  many  of  the  cells  the  plane  of 
section  has  not  passed  through  the  nucleus;  c,  intermuscular  septum  (connective  tissue); 
d,  smaU  artery. 

Voluntary  Striated  Muscle. — This  consists  of  cylindrical  fibres 
from  50  to  130  mm.  in  length  and  from  10  to  loops-  in  diameter. 
Generally  speaking,  the  fibres  of  greater  diameter  are  found  in  the 
larger  animals.  There  is  apparently  no  relation  between  the  size  of 
the  muscle  and  either  the  length  or  diameter  of  its  component  fibres. 
There  is  also  no  relation  of  length  to  diameter,  within  the  same 
muscle,  fibres  of  many  different  sizes  intermingling. 

Each  muscle  fibre  consists  of  (a)  a  delicate  sheath,  the sarcolemma , 
enclosing  (b)  the  muscle  substance  proper,  in  which  lie  (c)  the  muscle 
nuclei. 

The  sarcolemma  is  a  clear,  apparently  structureless,  very  elastic 
membrane,  which  adheres  so  closely  to  the  underlying  muscle  sub- 
stance as  to  be  indistinguishable  in  most  preparations.  In  teased 
specimens  it  may  frequently  be  seen  at  the  torn  ends  of  the  fibres 
(Fig.  58).  In  staining  reaction  it  differs  from  both  white  and  elastic 
tissue  and  is  apparently  to  be  considered  a  distinct  cell  membrane. 

The  muscle   substance    consists    of   ergasto plasm    (fibrillce)    and 


MUSCLE  TISSUE 


115 


sarcoplasm  (interjGibrillar  substance)  and  shows  two  sets  of  striations 
(Fig.  59),  longitudinal  striations  and  cross 
striations.  The  longitudinal  striations  are 
due  to  parallel  running  ultimate  fibrillae, 
which  lie  in  and  are  more  or  less  separated 
from  one  another  by  the  sarcoplasm.  Each 
fibrilla  when  examined,  unstained,  by  re- 
flected light  is  seen  to  be  composed  of  alter- 
nating Ught  and  dark  segments.  As  like 
segments  lie  in  the  same  transverse  plane, 
the  whole  muscle  fibre  appears  composed  of 
alternate  light  and  dark  bands  (Figs.  59 
and  60),  and  this  distinction  is  maintained 
even  in  stained  specimens,  as  the  light  bands 
stain  little  if  any,  with  most  staining  agents, 
while  the  dark  bands  react  strongly  to  stains. 
The  light  band  is  composed  of  a  singly  re- 
fracting (isotropic)  substance,  the  dark  band 
of  a  doubly  refracting  (anisotropic)  sub- 
stance. Through  the  middle  of  the  light 
band  runs  a  fine  line  (Krause's  line),  while 
an  even  finer  line  (Hensen^s  line)  can  some- 
times be  seen  running  through  the  middle 
lighter  portion  of  the  dark  band.  Both 
Krause's  and  Hensen's  lines  cross  the  inter- 
vening sarcoplasm  as  well  as  the  fibrillae  and 
extend  to  the  sarcolemma,  thus  completely 
crossing  the  fibre.  As  all  of  these  structures 
run  through  the  entire  thickness  of  the  fibre, 
they  in  reality  constitute  discs  of  muscle 
substance  (Fig.  60).  By  means  of  certain 
chemicals  these  discs  may  be  separated,  the 
separation  taking  place  along  the  lines  of 
Krause.  Each  "muscle  disc"  thus  consists 
of  that  portion  of  a  fibre  included  between 
two  adjacent  lines  of  Krause  and  is  com- 
posed of  a  central  dark  disc,  and  on  either 
side  one-half  of  each  adjacent  light  disc. 
A  muscle  fibre  is  thus  seen  to  be  divisible 
longitudinally  into  uUimale  fibrillce,  transversely  into  muscle  discs. 


Fig.  58. — Semidiagram- 
matic  Drawing  of  Parts  of 
two  Muscle  Fibres  which 
have  been  broken,  showing 
the  relations  between  Mus- 
cle Substance  Proper  and 
Sarcolemma  (Kanvier.) 
m,  a,  Retracted  ends  of 
muscle  substance,  between 
which  is  seen  the  sarcolem- 
ma with  several  adherent 
muscle  nuclei;  B,  thin  layer 
of  muscle  substance  which 
has  adhered  to  the  sarco- 
lemma; 71,  muscle  nucleus; 
s,  sarcolemma;  p,  space 
between  sarcolemma  and 
muscle  sul)stance. 


116 


THE  TISSUES 


What  is  known  as  the  sarcous  element  of  Bowman  is  that  portion 
of  a  single  fibrilla  which  is  included  in  a  single  disc,  i.e.,  between 
two  adjacent  lines  of  Krause  (Fig.  60). 

The  sarcoplasm  is  not  evenly  distributed  throughout  the  fibre. 
On  cross  section  irregular  trabeculae  of  sarcoplasm  are  seen  extend- 
ing in  from  the  sarcolemma  (Fig.  61).  These  separate  the  fibrillse 
into  bundles,  the  muscle  columns  of  Kolliker.     A  transverse  section 


V»« 


"iS 


d  ..... 


-  -b 


d  - 


Fig.  60. 
X350.     (Technic  4,  p. 


Fig.  59. 

Fig.  59. — Portion  of  Striated  Voluntary  Muscle  Fibre. 
125.)  The  fibre  is  seen  to  be  marked  transversely  by  alternate  light  and  dark  bands. 
Through  the  centre  of  the  light  band  is  a  delicate  dark  line  (Krause's  line) ;  through  the 
centre  of  the  dark  band  a  fine  light  indicates  Hensen's  line.  The  black  line  outlining 
the  fibre  represents  the  sarcolemma.  a,  Fibrillse;  h,  muscle  nucleus;  c,  Krause's  Hne; 
d,  Hensen's  line. 

Fig.  60. — Diagram  of  Structure  of  a  Muscle  Column  of  Kolliker.  The  appearance 
presented  by  the  cross-cut  muscle  column  =  Cohnheim's  field,  a,  Muscle  fibrillae;  h, 
sarcous  element;  c,  Krause's  line;  d,  Hensen's  line;  e,  Cohnheim's  field;  /,  muscle  disc. 

of  one  of  these  columns  presents  the  appearance  of  a  network  of 
sarcoplasm  and  of  interfibrillar  cement  substance  enclosing  the 
fibrillse.  This  appearance  is  known  as  Cohnheim's  field  (Figs.  60 
and  61). 

Many  of  the  details  of  structure  of  striated  muscle  have  been  determined  by 
studies  upon  the  muscles  of  lower  animals.  These  details  are  extremely  com- 
plicated and  the  numerous  terms  used  to  designate  the  same  structure  very  con- 


MUSCLE  TISSUE  117 

fusing.  The  following  is  the  scheme  of  structure  and  the  nomenclature  accord- 
ing to  Heidenhain  (Fig.  62). 

The  older  terms  muscle  cell  for  the  smooth  muscle  cell,  and  muscle  fibre  for 
the  analogous  mvdtinuclear  element  of  striated  muscle  are  retained,  also  Apathy's 
myofibril  for  the  ultimate  fibrilla,  Kolliker's  muscle  column  for  the  smallest  bun- 
dles of  fibrils,  and  sarcoplasm  for  interfibrillar  substance. 

The  muscle  fibre  is  subdivided  into  a  series  of  segments  by  transverse  discs 
which  completely  cross  the  fibre,  involving  both  fibrillse  and  sarcoplasm  and 
are  attached  to  the  sarcolemma.  This  disc  (ground  membrane — membrane  of 
Krause,)  Heidenhain  designates  the  telophragma  (Z).  That  part  of  a  fibre  which 
lies  between  two  telophragmata  is  an  iiwkomma.  The  middle  of  each  inokom- 
ma  is  crossed  by  a  disc  (Hensen's  membrane)  which  also  involves  both  fibrillae 


Fig.  61. — Semidiagrammatic  Drawing  of  Transverse  Section  of  a  Voluntary  Muscle 
Fibre,  showing  Sarcolemma;  sarcoplasm  separating  fibrils  into  bundles,  each  bundle 
constituting  a  muscle  column  of  KoUiker  and  the  appearance  of  its  cross-cut  end  being 
Cohnheim's  field,     a,  Sarcoplasm;  b,  Cohnheim's  fields;  c,  sarcolemma. 

and  sarcoplasm  and  is  attached  to  the  sarcolemma.  This  membrane  having 
apparently  the  same  structure  as  the  telophragma  is  designated  the  mesophragma 
(M).  The  mid-portion  of  the  inokomma  consists  of  anisotropic  substance 
(Q),  the  ends  of  isotropic  (J).  That  portion  of  Q  which  lies  on  either  side  of  M  is 
lighter  than  the  rest  of  Q  and  is  designated  Qh  (h  =  hell  =  clear) .  That  portion  of 
J  which  lies  close  on  either  side  of  Z  is  darker  than  the  rest  of  J  and  is  designated 
Jd  (d  =  dicht  =  thick).  In  the  sarcoplasm  between  the  fibrillae  are'granules;  those 
in  J  are  arranged  in  a  regular  row  and  are  known  as  J-granules,  those  in  Q  are 
more  irregularly  placed  and  arc  known  as  Q-granules.  In  Fig.  62  arc  also  shown 
the  "  cross-fibrc-nets "  which  arc  brought  out  by  metallic  impregnation  and 
which  possibly  represent  intracellular  canals. 

Two  varieties  of  striated  voluntary  muscle  fibres  are  distinguished, 
while  fibres  and  red  fibres.  The  difference  between  the  two  is  due 
to  the  amount  of  sarcoplasm — the  red  fibres  being  rich  in  sarcoplasm, 
the  white  fibres  poor.  Red  fibres  contract  less  rapidly  than  white, 
but  arc  less  easily  fatigued.  In  man  white  fibres  are  in  the  large 
majority,  red  fibres  never  occurring  alone,  but  mingled  with  white 
fibres  in  some  of  the  more  active  muscles,  such  as  those  of  respiration 


118 


THE  TISSUES 


and  mastication.     In  some  of  the  lower  animals  are  found  muscles 
made  up  wholly  of  red  fibres. 

Muscle  fibres  ending  within  the  substance  of  a  muscle  have 
pointed  extremities.     Where  muscle  fibres  join  tendon,  the  fibre  ends 


J^ 


yxs3K.-«ff^''' 


6-^ — 


Telophragma 
J-granules 


Oh 

M  — 


Qh 


J{    Jd 
Z 


/ 


•     M 


##    %  # 


z  -  ^  4j  _^i  pw  ^'^'n 


M     — - 


■!""'     K 


Q -granules 

Mesophragma 

Q-granules 

J-granules 
J-granules 


Cross-fibre 
nets 


Cross-fibre 
'    nets 


Fig.  62. — Scheme  of  Structure  of  Striated  Voluntary  Muscle  Fibre  with  Nomenclature 
of  Heidenhain.     (Heidenhain.) 

in  a  rounded  or  blunt  extremity,  the  sarcolemma  being  continuous 
with  the  tendon  fibres  (Figs.  63  and  64). 

Muscle  fibres  are  usually  unbranched.     In  some  muscles — e.g., 
those  of  the  tongue  and  of  the  eye — anastomosing  branches  occur. 


MUSCLE  TISSUE 


119 


^^. 


When  muscle  fibres  end  in  mucous  membranes 
— e.g.,  the  muscle  fibres  of  the  tongue— their 
terminations  are  often  branched. 

Muscle  fibres  are  multinuclear,  some  of  the 
large  fibres  containing  hundreds  or  even  thou- 
sands of  nuclei.^  In  the  white  fibres  the  nuclei 
are  situated  at  the  periphery  just  beneath  the 
sarcolemma.  In  red  fibres  they  are  centrally 
placed. 

Involuntary  Striated  Muscle  (Heart  Mus- 
cle).— This,  as  its  name  implies,  is  a  striated 
muscle  not  under  control  of  the  will.  It 
occurs  only  in  the  cardiac  musculature.  Like 
voluntary  muscle,  heart  muscle  is  striated 
both  longitudinally  and  transversely.  Like 
smooth  muscle,  on  the  other  hand,  it  is  com- 
posed of  units  which  at  least  resemble  cells  and 
have  long  been  called  heart  muscle  cells.  Heart 
muscle  also  resembles  smooth  muscle  in  that 
there  is  usually  but  one  nucleus  to  a  cell  and 
this  nucleus  is  centrally  placed  instead  of  lying 
at  the  periphery  as  in  voluntary  muscle.  Also 
the  sarcolemma  if  present  at  all  is  extremely 
delicate  and  is  probably,  as  in  smooth  muscle, 
only  a  modification  of  the  surface  sarcoplasm. 
The  amount  of  sarcoplasm  throughout  the  cell 
is  large.  Around  the  nucleus  is  an  area  of  sar- 
coplasm free  from  fibrillae.  This  area  often  ex- 
tends some  distance  toward  the  ends  of  the  cell. 

Heart  muscle  fibres  are  not  the  parallel- 
running  unbranched  fibres  of  voluntary  mus- 
cle, but,  while  having  a  generally  parallel 
arrangement,  give  off  side  branches  which 
anastomose,  making  it  impossible  to  trace  a 
single  fibre  for  any  great  distance.  These 
side  branches  have  the  same  structure  as  the 
main  fibre  except  that  they  are  for  the  most 
part  of  smaller  diameter  and  are  nonnucleated. 

*  Stiihr  calls  attention  to  the  fact  that  such  a  structure  may  be  considered  either  a 
multinuclear  cell  or  a  syncytium  and  that  there  is  really  no  true  distinction  between 
the  two. 


, c 


Fig.  63.  —  Semidia- 
grammatic  Illustration 
of  Endings  of  Muscle 
Fibres  within  a  Muscle 
and  in  Tendon, 
((iage.)  a,  Tapering 
end  of  fibre  terminating 
within  the  muscle;  the 
lower  end  of  the  central 
fibre  shows  the  same 
method  of  termination; 
c,  c,  each  fibre  termi- 
nates above  in  pointed 
intramuscular  ending, 
below  in  blunt  ending 
connected  with  tendon. 


120 


THE  TISSUES 


The  striations  of  heart  muscle  are  less  distinct  than  are  those  of 
voluntary  muscle,  but  apparently  represent  very  similar  structures. 
The  longitudinal  striations  indicate  fibrilla  lying  in  the  sarcoplasm. 
From  the  central  mass  of  sarcoplasm  which  surrounds  the  nucleus, 
strands  radiate  toward  the  periphery.  These  strands,  anastomosing, 
separate  the  fibrillse  into  columns,  the  muscle  columns  of  KolUker. 
In  cross  section  these  present  the  appearance  described  under  volun- 
tary muscle  as  Cohnheim' s  fields .     The  disposition  of  the  sarcoplasm, 


/ 


Fig.  6  s. 

Fig.  64. — Two  Muscle  Fibres  from  Upper  End  of  Human  Sartorius,  to  show  con- 
nection of  muscle  and  tendon.     X350.     (Gage.)     m,  Muscle  fibres;  t,  tendon  fibres. 

Fig.  65. — Muscle  Cells  from  the  Human  Heart  (technic  6,  p.  125),  showing  lateral 
branches  and  lines  of  union  between  cells.     Xsoo. 


extending  outward  from  the  region  of  the  nucleus  like  the  spokes  of  a 
wheel,  gives  to  the  cross  section  a  characteristic  radiate  appearance 
(Fig;  66),  not  seen  in  cross  sections  of  voluntary  muscle.  The 
transverse  markings  represent,  as  in  voluntary  muscle,  alternate 
light  and  dark  discs.  Through  the  middle  of  the  light  disc  can  be 
seen  the  membrane  of  Krause.  Mc Galium  describes  Krause's 
membrane  as  crossing  not  only  the  fibrillas,  but  also  the  sarco- 
plasm, as  in  the  voluntary  muscle  fibre.  The  sarcoplasm  he  describes 
as  further  subdivided  by  membranes,  which  are  transversely  con- 
tinuous with  Krause's  membranes,  into  minute  discs.     The  centre 


MUSCLE  TISSUE  121 

of  the  cell  around  the  nucleus  is  wholly  composed  of  these  little 
discs  of  sarcoplasm. 

Pecuhar  to  heart  muscle  are  what  appear  in  longitudinal  sections 
to  be  dark  lines  which  cross  transversely  both  main  fibres  and  side 
branches.  These  are  known  as  intercallated  discs  and  divide  the 
muscle  fibre  into  irregular,  short,  thick  cylindrical  segments.  A 
disc  may  pass  straight  across  a  fibre,  or  it  may  cross  it  in  a  series  of 
steps,  or  it  may  extend  only  part  way  across  the  fibre.  It  always 
touches  at  some  point  one  of  the  ground  membranes^  and  sometimes 


Fig.  66. — Section  of  Heart  Muscle.  X350.  (Technic  7,  p.  125.)  a,  Cells  cut 
longitudinally;  b,  cells  cut  transversely  (only  three  nuclei  have  Ijeen  included  in  the  plane 
of  section);  c,  ceUs  cut  obliquely;  d,  connective-tissue  septum. 

entirely  fills  the  space  between  two  ground  membranes  which  lie 
unusually  close  together.  Special  technic  has  demonstrated  the 
fact  that  the  fibrillae  do  not  stop  at  the  disc  but  are  continuous 
through  it,  although  they  show  in  passage  some  modification  of 
structure. 

The  one  question  which  has  been  most  discussed  in  rcgcard  to  the  structure 
of  heart  muscle  and  which  remains  still  unanswered  is  whether  heart  muscle  is 
cellular  or  a  syncytium.  The  solution  of  the  problem  is  of  course  dependent 
upon  the  determination  of  the  significance  of  the  intercallated  discs — whether  or 
not  they  represent  true  cell  boundaries.  The  segments  into  which  the  heart 
muscle  fibre  is  divided  by  the  discs  have  long  been  described  as  cells.  The  fact 
that  the  nuclei  are  usually  placed  about  midway  between  two  discs;  that  the 
discs  show  the  same  staining  reaction  as  intercellular  substance  when  subjected 
to  the  action  of  silver  nitrate,  and  the  ease  with  which  heart  muscle  may  be 

'  Some  authorities  deny  this. 


122 


THE  TISSUES 


separated  into  "cells,"  especially  in  young  animals  and  in  lower  vertebrates,  by 
use  of  those  chemicals  usually  used  to  break  down  intercellular  cement;  have  all 
been  used  as  arguments  in  favor  of  a  cellular  structure.  On  the  other  hand,  the 
fact  that  it  has  not  been  proved  that  the  segments  bounded  by  the  discs  corre- 
spond to  the  original  myoblasts;  that  in  the  later  stages  of  development  of  heart 
muscle  the  type  of  nuclear  division  is  usually  amitotic,  a  type  frequently  unac- 
companied by  division  of  the  cytoplasm;  that  the  fibrill«  pass  uninterrupted 
through  the  discs;  that  some  discs  only  partially  cross  a  fibre;  that  some  segments 
contain  more  than  one  nucleus  while  others  are  non-nucleated;  all  favor  a 
syncytial  interpretation.  How  open  the  question  still  remains  is  shown  by  the 
fact  that  Heidenhain  regards  the  "ceUs"  as  "growth  segments";  that  Marceau 
considers  them  non-contractUe  "supports"  for  the  fibriUae;  that  Jordan  from 
his  work  on  humming-birds  concludes  that  they  are  a  coarser  development  of 
the  anisotropic  bands;  while  Schaffer  looks  upon  them  as  post-mortem  contrac- 
tion artefacts. 

Development  oe  Muscle  Tissue 

Smooth  Muscle. — In  the  higher  animals,  muscle  tissue  with  the  exception  of 
that  connected  with  the  sweat,  lacrymal  and  mammary  glands,  which  is  of 


Fig.  67. — Myoblasts  in  DifEerent  Stages  of  Development.     (Godlewski.) 
The  upper  cell  represents  a  myoblast  with  granular  cytoplasm  (from  sheep  embryo 
of  13  mm.) ;  the  middle,  a  myoblast  with  fibrils  in  process  of  formation  (from  guinea-pig 
embryo  of  10  mm.);  the  lower,  a  myoblast  with  still  further  differentiated,  segmented 
fibrils  (from  a  rabbit  embryo  of  8.5  mm.). 

ectodermic  origin,  is  derived  wholly  from  mesoderm.  The  cells  (myoblasts) 
which  are  to  become  smooth  muscle  cells  develop  in  the  general  mesenchymal 
tissue  among  cells  which  are  to  become  connective-tissue  cells  and  with  which 
they  are  at  first  apparently  identical.  In  becoming  a  smooth  muscle  ceU  the 
myoblast  changes  its  shape,  becoming  greatly  elongated,  its  nucleus  at  the  same 
time  becoming  oval  or  rod  shaped.  Such  cells  anastomose  freely.  During  these 
changes  in  shape,  delicate  longitudinal  fibrils  appear  in  the  cytoplasm.  Just 
how  these  fibrils  originate  is  not  known,  but  they  probably  represent  a  speciali- 
zation and  rearrangement  of  the  spongioplasm. 

Striated  Vohmtary  Muscle. — This  develops  from  the  mesoblastic  somites. 
Each  somite  early  divides  into  an  outer  part,  sclerotome  or  cutis  plate,  and  an  inner 
part,  the  myotome  or  muscle  plate.     Cells  of  the  myotome  soon  show  changes 


MUSCLE  TISSUE 


123 


which  distinguish  them  as  mj'oblasts  or  muscle-forming  cells.  These  cells,  which 
are  at  first  spherical,  become  elongated  and  spindle  shaped.  The  nucleus  is  at 
this  stage  centrally  placed  and  the  spongioplasm  is  in  the  form  of  a  reticulum. 


'^■\ 


w    .  - 

Fig.  68. — From  a  Section  of  Developing  Heart  Muscle  from  a  Rabbit  Embryo  of  9 

mm.     (Godlewski.) 

a,  Cell  body  with  granules  arranged  in  series;  b,  cell  body  with  centrosome  and  attrac- 
tion sphere;  c,  branching  fibril;  d,  fibrils  extending  through  several  cells. 

Fibrillar  arrangement  of  the  spongioplasm  first  appears  around  the  periphery 
where  granules  form  in  the  cytoplasm  and  become  arranged  in  rows  lengthwise 
of  the  cell.    The  central  portion  of  the  cell  is  at  this  stage  still  occupied  by  retic- 


'"""^j^V'^j*^  -v^  """ 


xi:*'j-^-- 


':::z^© 


,.«a»*»**J****^-^V'  ,,  ^ 


Fig.  69. — From  a  Section  oi  I  developing  iicarL  Aiuscle  in  a  Kaijbit  i'-mbryo  of  10  mm. 

(Godlewski.) 
The  fibrils  are  segmented,  indicating  the  beginning  of  the  cross  striation  charactis- 

tic  of  heart  muscle. 

ular  spongioplasm  and  the  nucleus.  These  granules  next  unite  to  form  deli- 
cate fibrils.  New  fibrils  form  both  by  longitudinal  arrangement  of  more  granules 
and  by  longitudinal  splitting  of  fibrils  already  formed,  until  they  finally  fill 


124  THE  TISSUES 

the  entire  cell.  After  the  union  of  the  granules  to  form  fibrils  the  latter  are 
apparently  homogeneous,  but  later  differentiate  into  the  alternate  light  and  the 
dark  substances  which  determine  the  cross  striations  characteristic  of  striated 
muscle.  Just  how  this  differentiation  takes  place  is  not  known.  During  this 
process  of  fibrillation  the  nucleus  has  been  undergoing  mitotic  division  without 
corresponding  division  of  the  cytoplasm.  In  white  fibres  these  nuclei  migrate 
to  the  surface  and  come  to  lie  just  beneath  the  sarcolemma.  The  sarcoplasm  in 
which  the  fibrils  lie  probably  represents  the  remains  of  the  undifferentiated  pro- 
toplasm (hyaloplasm). 

Some  authorities  deny  the  origin  of  the  musde  fibre  from  a  single  cell,  describ- 
ing it  as  derived  from  a  number  of  myoblasts  which  unite  to  form  a  fibre. 

Heart  muscle  develops  from  mesenchyme.  The  myoblasts  are  at  first  small, 
spheroidal,  and  closely  arranged.  With  the  appearance  of  intercellular  substance 
the  cells  become  separated  and  irregular  in  shape,  and  anastomose  to  form  a  syn- 
cytium. A  little  later  the  cells  become  arranged  in  parallel  columns  and  cross 
markings,  the  " intercaUated  discs"  appear,  dividing  the  syncytium  into  the 
so-called  "heart-muscle  cells."  Whether  these  coincide  with  the  original  myo- 
blasts is  not  known.  As  in  voluntary  muscle,  fibrils  first  develop  in  the  periphery 
of  the  cell  apparently  by  union  of  granules  which  arrange  themselves  in  lines 
lengthwise  of  the  cell.  The  fibrils  increase  in  number  and  invade  the  entire 
cell  except  the  small  area  of  undifferentiated  protoplasm  which  remains  around 
the  nucleus.  Later  the  fibrils  show  the  alternate  light  and  dark  markings  or  cross 
striations.  As  with  voluntary  muscle  the  way  in  which  these  cross  markings' 
develop  is  not  known. 

Attention  has  already  been  called  (p.  52)  to  the  spongioplasm  as  the  con- 
tractile element  of  protoplasm.  It  is  to  be  noted  that  in  the  development  of 
muscle  no  new  element  appears,  the  contractile  fibrillce  representing  nothing  more 
than  a  specialization  of  the  already  contractile  spongioplasm. 

TECHNIC 

(i)  Isolated  Smooth  Muscle  Cells. — Place  small  pieces  of  the  muscular  coat 
of  the  intestine  in  o.i-per-cent.  aqueous  solution  of  potassium  bichromate,  or  in 
30-per-cent.  alcohol  for  forty-eight  hours.  Small  bits  of  the  tissue  are  teased 
thoroughly  and  mounted  in  glycerin.  Nuclei  may  be  demonstrated  by  first 
washing  the  tissue  and  then  staining  for  twelve  hours  in  alum  carmine  (p.  19). 
This  is  poured  off,  the  tissue  again  washed  in  water  and  preserved  in  eosin-glyc- 
erin,-  which  gives  a  pink  color  to  the  cytoplasm. 

(2)  Potassium  hydrate  in  40-per-cent.  aqueous  solution  is  also  recommended 
as  a  dissociater  of  smooth  muscle  cells.  Pieces  of  the  muscular  coat  of  the  intes- 
tine are  placed  in  this  solution  for  five  minutes,  then  transferred  to  a  saturated 
aqueous  solution  of  potassium  acetate  containing  i-per-cent.  hydric  acetate  for 
ten  minutes.  Replace  the  acetate  solution  by  water,  shake  thoroughly,  allow 
to  settle,  pour  off  water,  and  add  alum-carmine  solution  (p.  19).  After  twelve 
hours'  staining,  wash  and  transfer  to  eosin-glycerin. 

(3)  Sections  of  Smooth  Muscle. — Fix  small  pieces  of  intestine  in  formalin- 
MiiUer's  (technic  5,  p.  7)  or  in  Zenker's  fluid  (technic  9,  p.  8).     Thin  transverse 


MUSCLE  TISSUE  125 

or  longitudinal  sections  are  stained  with  haematoxylin-eosin  (technic  i,  p.  20), 
and  mounted  in  balsam.  As  the  two  muscular  coats  of  the  intestine  run  at  right 
angles  to  each  other,  both  longitudinally  and  transversely  cut  muscle  may  be 
studied  in  the  same  section. 

(4)  Striated  \'oluntary  JMuscle  Fibres. — One  of  the  long  muscles  removed 
from  a  recently  killed  animal  is  kept  in  a  condition  of  forced  extension  while  a  i- 
per-cent.  aqueous  solution  of  osmic  acid  is  injected  into  its  substance  at  various 
points  by  means  of  a  hypodermic  syringe.  Fixation  is  accomplished  in  from 
three  to  five  minutes.  The  parts  browned  by  the  osmic  acid  are  then  cut  out 
and  placed  in  pure  glycerin,  in  which  they  are  teased  and  mounted. 

(5)  Sections  of  Striated  \'oluntary  Muscle. — Fix  a  portion  of  a  tongue  in 
formalin- ]M tiller's  fluid  or  in  Zenker's  fluid  (p.  8).  Thin  sections  are  stained 
with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  21)  and  mounted  in  balsam. 
As  the  muscle  fibres  of  the  tongue  run  in  aU  directions,  fibres  cut  transversely, 
longitudinally,  and  obliquely  may  be  studied  in  the  same  section.  The  sarco- 
lemma,  the  pointed  endings  of  the  fibres,  and  the  relation  of  the  fibres  to  the  con- 
nective tissue  can  also  be  seen. 

(6)  Isolated  heart-muscle  cells  may  be  obtained  in  the  same  manner  as  smooth 
muscle  cells.     (See  technic  i,  p.  124.) 

(7)  Sections  of  Heart  Muscle. — These  are  prepared  according  to  technic  3 
(above).  By  including  the  heart  wall  and  a  papillary  muscle  in  the  same  section, 
both  longitudinally  and  transversely  cut  cells  are  secured.  The  stain  may  be 
either  haematoxylin-eosin  (technic  i,  p.  20),  or  haematoxylin-picro-acid-fuchsin 
(technic  3,  p.  21). 


CHAPTER  VI 
NERVE  TISSUE 

The  Neurone 

In  most  of  the  cells  thus  far  described  the  protoplasm  has  been 
confined  to  the  immediate  vicinity  of  the  nucleus.  In  the  smooth 
muscle  cell  was  seen  an  extension  of  protoplasm  to  a  considerable 
distance  from  the  nuclear  region,  while  in  the  connective-tissue  cells 
of  the  cornea  the  protoplasmic  extensions  took  the  form  of  distinct 
processes.  Processes,  often  extending  long  distances  from  the  cell 
body  proper,  constitute  one  of  the  most  striking  features  of  nerve- 
cell  structure.  Some  of  these  processes  are  known  as  nerve  fibres; 
and  nerve  tissue  was  long  described  as  consisting  of  two  elements, 
nerve  cells  and  nerve  fibres.  With  the  establishment  of  the  unity  of 
the  nerve  cell  and  the  nerve  fibre,  the  nerve  cell  with  its  processes 
was  recognized  as  the  single  structural  unit  of  nerve  tissue.  This 
unit  of  structure  is  known  as  a  neurone.  The  neurone  may  thus  be 
defined  as  a  nerve  cell  with  all  of  its  processes. 

In  the  embryo  the  neurone  is  developed  from  one  of  the  ectoder- 
mic  cells  which  ccnstitute  the  wall  of  the  primitive  neural  canal. 
This  embryonic  nerve  cell,  or  neuroblast,  is  entirely  devoid  of  proc- 
esses. Soon,  however,  frcm  one  end  of  the  cell  a  process  begins  to 
grow  out.  This  process  is  known  as  the  axone  (axis-cylinder  process, 
neuraxone,  neurite).  Other  processes  appear,  alf'o  as  outgrowths  of 
the  cell  body;  these  are  known  as  protoplasmic  processes  or  dendrites. 

Each  adult  neurone  thus  consists  of  a  cell  body,  and  passing  off 
from  this  cell  body  two  kinds  of  processes,  the  axis-cylinder  process 
and  the  dendritic  processes  (Fig.  70) . 

An  impoitant  exception  to  this  rule  is  presented  by  the  cells  of  the  cerebro- 
spinal ganglia  (Fig.  292).  Here  the  typical  neurone  has  two  processes,  a  periph- 
eral process,  and  a  central  process  which  enters  the  central  nervous  system. 
Both  processes  have  a  typical  axis-cylinder  structure.  Some  authorities  have 
interpreted  the  peripheral  process  as  a  modified  dendrite. 

I.  The  Cell  Body. — Like  most  other  cells,  the  nerve  cell  body 
consists  of  a  mass  of  protoplasm  surrounding  a  nucleus  (Fig.  71), 

126 


NERVE  TISSUE 


127 


Nerve  cell  bodies  vary  in  size  from  very  small  cell  bodies,  such  as 
those  found  in  the  granule  layers  of  the  cerebellum  and  of  the  olfac- 
tory lobe,  to  the  large  bodies  of  the  Purkinje  cells  of  the  cerebellum 

and  of  the  motor  cells  of  the  ventral 
horns  of  the  cord,  which  are  among  the 
largest  in  the  body.  There  is  as  much 
variation  in  shape  as  in  size,  and  some 
of  the  shapes  are  characteristic  of  the 
regions  in  which  the  cells  are  situated. 
Thus,  many  of  the  bodies  of  the  cells 

w 

Ml 


Fig.  70.  Fig.  71. 

Fig.  70. — Scheme  of  Peripheral  JMotor  Neurone.  (Barker.)  The  cell  body, 
protoplasmic  processes,  axone,  collaterals,  and  terminal  arborizations  in  muscle  are  all 
seen  to  be  parts  of  a  single  cell  and  together  constitute  the  neurone,  c,  Cytoplasm  of 
cell  body  containing  chromophilic  bodies,  neurofibrils,  and  perifibrillar  substance;  n, 
nucleus;  «',  nucleolus;  d,  dendrites;  ah,  axone  hill  free  from  chromophilic  bodies; 
ax,  axone;  sf,  branch  (collateral;;  m,  medullary  sheath;  n  R,  node  of  Ranvier  where 
branch  is  given  ofT;  si,  neurilemma  (probably  not  present  in  central  nervous  system); 
m',  striated  muscle  fibre;  lei,  motor  end  plate. 

Fig.  7  r. — Large  Motor  Nerve  Cell  from  Ventral  Horn  of  Spinal  Cord  of  Ox,  showing 
Chromophilic  Bodies.  (From  Barker,  after  von  Lenhossek.)  <7,  Pigment;  h,  axone; 
c,  axone  hill;  d,  dendrites. 

of  the  spinal  ganglia  are  spheroidal;  of  most  of  the  cells  of  the  cortex 
cerebri,  pyramidal;  of  the  cells  of  Purkinje,  pyriform;  of  the  cells  of 
the  ventral  horns  of  the  cord,  irregularly  stellate.  According  to  the 
number  of  processes  given  off,  nerve  cells  are  often  referred  to  as 
unipolar,  bipolar,  or  multipolar. 

The  NUCLEUS  of  the  nerve  cell  (Fig.  71)  differs  in  no  essential 


128 


THE  TISSUES 


from  the  typical  nuclear  structure.  It  consists  of  (i)  a  nuclear  mem- 
brane, (2)  an  intranuclear  network  of  linin  and  chromatin,  (3)  an 
achromatic  nucleoplasm,  and  (4)  a  nucleolus. 

The  CYTOPLASM  of  the  nerve  cell  consists  of  at  least  two  distinct 
elements:  (i)  Neurofibrils,  and  (2)  perifibrillar  substance.  In  most 
nerve  cells  a  third  element  is  present,  (3)  chromophilic  bodies. 


'^^v 


Fig.  72. — Ganglion  Cells,  Stained  by  Bathe's  Method,  showing  Neurofibrils.  A 
Anterior  horn  ceU  (human);  B,  ceU  from  facial  nucleus  of  rabbit;  C,  dendrite  of  human 
anterior  horn  cell  showing  arrangement  of  neurofibrils.  (Bethe.)  In  B  the  chromophilic 
bodies  are  shown.     In  this  picture  the  neurofibrils  are  shown  as  not  anastomosing. 


(i)  The  neurofibrils  are  extremely  delicate  fibrils  which  are  con- 
tinuous throughout  the  cell  body  and  all  of  its  processes.  Within 
the  body  of  the  cell  they  cross  and  interlace  and  probably  anastomose 
(Figs.  72  and  73). 

(2)  The  perifibrillar  substance  (Fig.  72)  is  a  fluid  or  semi-fluid 
substance  which  both  in  the  cell  body  and  in  the  processes  surrounds 


NERVE  TISSUE 


129 


and  separates  the  neurofibrils.  It  is  believed  by  some  to  be  like 
the  fibrils,  continuous  throughout  the  cell  body  and  processes,  by 
others  to  be  interrupted  at  certain  points  in  the  axone  (see  p.  137). 

(3)  The  chromophilic  bodies  (Fig.  71)  are  granules  or  groups  of 
granules  which  occur  in  the  cytoplasm  of  all  of  the  larger  and  of 
many  of  the  smaller  nerve  cells.  They  are  best  demonstrated  by 
means  of  a  special  technic  known  as  the  method  of  Nissl  (page  38). 


\ 


Fig.  73. — Body  of  Large  Pyramidal  Cell  from  Cortex  of  Cat.  Silver  Method  of 
Cajal.  Shows  nucleus  pale  and  arrangement  of  neurofibrils  within  the  cell;  a,  axone; 
b,  main  or  apical  dendrite.  (Cajal).  In  this  picture  the  neurofibrils  are  shown  as 
anastomosing. 

When  subjected  to  this  technic,  nerve  cells  present  two  very  dif- 
ferent types  of  reaction.  In  certain  small  cells  the  amount  of 
cytoplasm  is  extremely  small  and  only  the  nuclei  stain  with  the 
Nissl  method.  Such  cells  are  found  in  the  granule  layers  of  the 
cerebellum,  olfactory  l(;be,  and  retina.  They  are  known  as  caryo- 
chrome  cells,  and  apparently  consist  wholly  of  neurofibrils  and  peri- 
fibrillar substance.  Other  cells  react,  both  as  to  their  nuclei  and  as 
to  their  cell  bodies,  to  the  Nissl  stain.  These  cells  are  known  as 
somalochrome  cells.  Taking  as  an  example  of  this  latter  type  of  cell 
one  of  the  motor  cells  of  the  ventral  horn  of  the  cord  and  subjecting 
0 


130 


THE  TISSUES 


it  to  the  Nissl  technic,  we  note  that  the  cytoplasm  is  composed  of 
two  distinct  elements:  (a)  a  clear,  unstained  ground  substance,  and, 
scattered  through  this,  (&)  deep-blue-staining  masses,  the  chromo- 

These  bodies  are  granular  in  character  and 


philic  bodies  (Fig.  71). 


Fig.  74. — Pyramidal  Cell 
from  Huro.an  Cerebral  Cortex. 
(Golgi  bichlorid  method.  See 
2,  p.  36.)  Golgi  cell  type  I. 
a,  Cell  body;  b,  main  or  apical 
dendrite  showing  gemmules; 
c,  lateral  dendrites  showing 
gemmules;  d,  axone  with  col- 
laterals. Only  part  of  axone 
is  included  in  drawing. 


differ  in  shape,  size,  and  arrangement. 
They  may  be  large  or  sm.all,  regular  or 
irregular  in  shape,  may  be  arranged  in 
rows  or  in  an  irregular  manner,  may  be 
close  together,  almost  filling  the  cell  body, 
or  quite  separated  from  one  another. 
Presenting  these  variations  in  different 
types  of  cells,  the  appearance  of  the 
chromophilic  bodies  in  a  particular  type 
of  cell  remains  constant,  and  has  thus  been 
used  by  Nissl  as  a  basis  of  classification.^ 

It  is  important  to  note  in  studying  the 
nerve  cell  by  this  method  that  somato- 
chrome  cells  of  the  same  type  frequently 
show  marked  variations  in  staining  in- 
tensity. This  appears  to  depend  upon 
the  size  and  closeness  of  arrangement  of 
the  chromophilic  bodies,  and  this  again 
seems  dependent  upon  changes  in  the 
cytoplasm  connected  with  functional  ac- 
tivity. 

In  cells  stained  by  Nissl's  method  the 
cytoplasm  between  the  chromophilic 
bodies  remains  unstained  and  apparently 
structureless,  and  it  is  this  part  of  the 
cytoplasm  that  corresponds  to  the  neuro- 
fibrils and  a  part  at  least  of  the  perifibril- 
lar substance. 


The  relation  which  the  appearance  of  the  Nissl-stained  cell  bears  to  the 
structure  of  the  living  protoplasm  is  still  undetermined.  According  to  some 
investigators  the  Nissl  bodies  exist  as  such  in  the  living  cell.  Others  believe 
that  they  are  not  present  in  the  living  cell,  but  represent  precipitates  due 
either  to  postmortem  changes  or  to  the  action  of  fixatives.  The  significance 
of  the  Nissl  picture  from  the  standpoint  of  pathology  lies  in  the  fact  that 
when  subjected  to  a  given  technic,  a  particular  type  of  nerve  cell  always  pre- 

■     ^  For  this  classification,  the  signiiicance  of  which  is  somewhat  doubtful,  the  reader 
is  referred  to  Barker,  "The  Nervous  System  and  Its  Constituent  Neurones,"  p.  121. 


NERVE  TISSUE  •    131 

sents  the  same  appearance  ("equivalent  picture"),  and  that  this  appearance 
furnishes  a  norm  for  comparison  with  cells  showing  pathological  changes,  and 
which  have  been  subjected  to  the  same  technic. 

Many  nerve  cells  contain  more  or  less  brownish  or  yellowish 
pigment  (Fig.  71).  This  pigment,  which  is  a  lipochrome,  is  not 
present  in  the  cells  of  the  ^new-born,  but  appears  in  increasing 
amounts  with  age.  Its  significance  is  not  known.  Another  black 
pigment  known  as  melanin  is  present  in  certain  cells  in  the  central 
nervous  system  (e.g.,  the  substantia  nigra).  This  pigment  is  said 
to  increase  in  amount  until  adolescence. 


Fig.  75. — Golgi  Cell  Type  II.  from  Cerebral  Cortex  of  Cat.  (Kolliker.)  a;,  Coarse 
protoplasmic  processes  with  gemmules  easily  distinguishable  from  the  more  delicate, 
smoother  axone,  a.  The  latter  is  seen  breaking  up  into  a  rich  plexus  of  terminal  fibres 
near  its  cell  of  origin,  practically  the  entire  neurone  being  included  in  the  drawing. 

In  addition  to  its  characteristic  structure,  the  nerve  cell  may 
contain  many  elements  found  in  other  cells  (p.  43).  Golgi,  Holm- 
gren, Cajal,  and  others  have  also  demonstrated  a  network  of  canals 
within  the  nerve  cell  similar  to  that  found  in  other  cells  (p.  46,  Fig.  4). 

n.  The  Protoplasmic  Processes  or  Dendrites. — These  have  a 
structure  similar  to  that  (;f  the  cell  body,  consisting  of  neurofibrils, 
perifibrillar  substance,  and,  in  somatochrome  cells,  chromophiUc 
bodies  (Figs.  71  and  72).     Dendrites  branch  dichotomously,  become 


132  THE  TISSUES 

rapidly  smaller,  and  usually  end  at  no  great  distance  from  the  cell 
body  (Figs.  74  and  75). 

III.  The  Axone.- — This  differs  from  the  cell  body  and  dendrites 
in  that  it  contains  no  chromophilic  bodies  (Fig.  71),  consisting 
wholly  of  neurofibrils  and  perifibrillar  substance.  Not  only  is  it 
entirely  achromatic  itself,  but  it  always  takes  origin  from  an  area 
of  the  cell  body,  the  axone  hill  (Fig.  71),  which  is  also  free  from 
chromophilic  bodies.  It  is  as  a  rule  single,  and  while  usually  arising 
from  the  body  of  the  cell  may  be  given  off  from  one  of  the  larger 
protoplasmic  trunks.  Some  few  cells  have  more  than  one  axone, 
and  nerve  cells  without  axones  have  been  described.  In  Golgi 
preparations  the  axone  is  distinguished  by  its  straighter  course, 
more  uniform  diameter,  and  smoother  outline  (Fig.  74).  It  sends 
off  few  branches  {collaterals),  and  these  approximately  at  right  angles. 
Both  axone  and  collaterals  usually  end  in  terminal  arborizations. 
In  most  cells  the  axone  extends  a  long  distance  from  the  cell  body. 
Such  cells  are  known  as  Golgi  cell  type  I  or  long  axone  neurones 
(Fig.  74).  In  others  the  axone  branches  and  ends  in  the  gray  matter 
in  the  vicinity  of  its  cell  of  origin — Golgi  cell  type  II  or  short  axone 
neurones  (Fig.  75). 

As  they  leave  the  cell  body  the  neurofibrils  of  the  axone  converge 
to  a  very  narrow  portion  of  the  axone,  where  the  perifibrillar  sub- 
stance is  much  reduced  in  amount,  or  according  to  some,  entirely 
interrupted.  Beyond  this  the  fibrils  become  more  separated  and 
the  perifibrillar  substance  more  abundant. 

Some  axones  pass  from  their  cells  of  origin  to  their  terminations 
as  "naked"  axones,  i.e.,  uncovered  by  any  sheath.  Other  axones 
are  enclosed  by  a  thin  membrane,  the  neurilemma  or  sheath  of 
Schwann.  Still  others  are  surrounded  by  a  sheath  of  considerable 
thickness  known  as  the  medullary  or  myelin  sheath. 

Depending  upon  the  presence  or  absence  of  a  medullary  sheath, 
axones  may  thus  be  divided  into  two  main  groups — medullated 
axones  and  non-medullated  axones. 

I.  Non-medullated  Axones  (non-medullated  nerve  fibres)  (Fig. 
76).  These  are  subdivided  into  non-medullated  axones  without  a 
neurilemma  and  non-medullated  axones  with  a  neurilemma. 

(a)  Non-medullated  axones  without  a  neurilemma  are  merely 
naked  axones.  Present  in  large  numbers  in  the  embryo,  they  are 
in  the  adult  confined  to  the  gray  matter  and  to  the  beginnings  and 
endings  of  sheathed  axones,  all  of  the  latter  being  uncovered  for  a 


NERVE  TISSUE 


133 


short  distance  after  leaving  the  nerve  cell  body,  and  also  just  before 
reaching  their  terminations. 

{b)  Non-meduUated  axones  with  a  neurilefnma — fibres  of  Remak 
(Fig.  76).  In  these  the  axone  is  surrounded  by  a  delicate  homo- 
geneous, nucleated  sheath,  the  neurilemma  or  sheath  of  Schwann 
(see  p.  135).     These  axones  are  described  by  some  writers  as  having 


A 


I         -  "/III  11 

Fig.  76.  Fic.   7  7. 

Fig.  76. — Non-meduUated  Ncr\-e  Fibres  with  Neurilemma,  only  the  nuclei  of  which 
can  be  seen.     X300. 

Fig.  77. — A,  Fresh  nerve  fibre  from  sciatic  nerve  of  rabbit  teased  apart  in  normal 
salt  solution,  showing  broad  unshrunken  axone  and  comparatively  thin  medullary 
sheath.  B,  Showing  crenation  of  medullary  sheath  which  occurs  soon  after  placing 
fibres  in  salt  solution.  C,  Same  after  fixation  and  staining  with  picro-acid-fuchsin, 
showing  shrunken  axone  and  broad  medullary  space.  The  latter  usually  contains 
irregular  clumps  of  myelin,  a,  Node  of  Ranvier;  b,  incisures  of  Schmidt;  c,  nucleus  of 
neurilemma. 


no  true  neurilemma,  but  merely  a  discontinuous  covering  of  flat 
connective-tissue  cells,  which  wrap  around  the  axone  and  corre- 
spond to  the  end(meurium  of  the  nerve  trunk  (see  page  426).  The 
majority  of  the  axones  of  the  cells  of  the  sympathetic  ganglia  fall 
under  this  category. 

2.  Meuullated  Axones  (mcduUatcd  or  myelinated  nerve  fibres). 
— The.se,  like  the  non-medullated,  are  subdivided  according  to  the 


134 


THE  TISSUES 


presence  or  absence  of  a  neurilemma  into  meduUated  axones  with  a 
neurilemma  and  meduUated  axones  without  a  neurilemma. 

(a)  MeduUated  axones  with  a  neurilemma  constitute  the  bulk 
of  the  fibres  of  the  cerebro-spinal  nerves.  Each  fibre  consists  of 
(i)  an  axone  or  axis-cylinder,  (2)  a  medullary  sheath,  and  (3)  a 
neurilemma. 

(i)  The  axone  is  composed  of  neurofibrils  continuous  with  those 
of  the  cell  body,  and  like  them  lying  in  a  perifibrillar  substance  or 
neuroplasm  (Fig.  82).     In  the  fresh  condition  the  axone  is  broad, 


Fig.  78. — I,  Fibres  of  Remak;  2,  nerve  fibre  from,  central  nervous  system  (medul- 
lated  but  without  sheath  of  Schwann) ;  3  and  4,  nerve  fibres  from  the  sciatic  of  frog, 
showing  nodes  of  Ranvier,  and  in  4  the  incisures  of  Schmidt. 

and  shows  faint  longitudinal  striations  corresponding  to  the  neuro- 
fibrils, or  appears  homogeneous  (Fig.  77,  A).  Fixatives  usually 
cause  the  axone  to  shrink  down  to  a  thin  axial  thread,  whence  its 
older  name  of  axis-cylinder  (Fig.  77,  C).  A  delicate  membrane 
has  been  described  by  some  as  enveloping  the  axone.  It  is  known 
as  the  axolemma  or  periaxial  sheath  (Fig.  80). 

(2)  The  medullary  sheath  (Figs.  77  and  82)  is  a  thick  sheath 
largely  composed  of  a  semi-fluid  substance  resembling  fat  and  known 
as  myelin.  In  the  fresh  state  the  myelin  has  a  glistening  homo- 
geneous appearance.  It  is  not  continuous,  but  is  divided  at  intervals 
of  from  80  to  6co/i  by  constrictions,  the  nodes  or  constrictions  of 
Ranvier.  That  portion  of  a  fibre  included  between  two  nodes  is 
known  as  an  internode  (Fig.  80).     The  length  of  the  internode  is 


NERVE  TISSUE 


135 


usually  proportionate  to  the  size  of  the  jSibre,  the 
smaller  hbres  having  the  shorter  internodes.  In 
fresh  specimens  the  medullary  sheath  of  an  inter- 
node  appears  continuous  (Fig.  yj,  A),  but  in  fixed 
specimens  it  is  broken  up  into  irregular  segments, 
Schmidt-La  titer  ma  nn  segments,  by  clefts  which 
pass  from  neurilemma  to  the  axolemma  or  axone, 
and  are  known  as  the  clefts  or  incisures  of  Schmidt- 
Lantermann  (Fig.  77,  C).  On  boiling  medullated 
nerve  fibres  in  alcohol  and  ether  a  fine  network 
is  brought  out  in  the  medullary  sheath,  the 
neurokeratin  network.  Owing  to  the  resistance  of 
neurokeratin  to  the  action  of  trypsin,  it  has  been 
considered  as  possibly  similar  in  composition  to 
horn. 

(3)  The  neurilemma  or  sheath  of  Schwann 
(Figs.  82,  B,  and  81)  is  a  delicate  structureless 
membrane  which  encloses  the  myelin.  At  the 
nodes  of  Ranvier  the  neurilemma  dips  into  the 
constriction  and  comes  in  contact  with  the  axone 
or  axolemma.  Silver  nitrate  staining  shows  a 
black  transverse  line  in  the  neurilemma  at  the 
node  of  Ranvier.  This  line  represents  the  bound- 
ary between  two  neurilemma  cells.  Against  the 
inner  surface  of  the  neurilemma,  usually  about 
midway  between  two  nodes,  is  an  oval-shaped 
nucleus,  the  nucleus  of  the  neurilemma  (Figs.  76, 
C,  and  81).  Each  nucleus  is  surrounded  by  an 
area  of  granular  protoplasm,  and  makes  a  little 
depression  in  the  myelin  and  a  sHght  bulging  of 
the  neurilemma  (Fig.  77,  C).  According  to  most 
observers  no  neurilemma  is  present  in  the  central 
nervous  system.  An  important  exception  is 
Cajal,  who  describes  the  medullated  fibre  of  the 
central  nervous  system  as  having  a  neurilemma. 

In  addition  to  the  above-described  sheaths, 
most  medullated  fibres  of  peripheral  nerves  have. 


Fi<;.  79. — Dia- 
grammatic Repre- 
scntalion  of  Portions 
of  Two  Medullated 
Nerve  Fibres,  as  seen 
in  Longitudinal  Sec- 
tion, stained  with 
OsmicAcid.  (Length 
of  intcrnode  is  pro- 
portionately short- 
_  encd.)     /i,^,  Nodes 

~  of  Ranvier,  with  axis 

cylinder  passing  through;  n,  neurilemma;  c,  nucleus  surrounded  by  protojjlasm, 
lying  at  about  the  middle  of  the  internode  between  the  neurilemma  and  the  mccluliary 
sheath.     (From  drawing  by  J.  F.  \eale  in  Quain's  Anatomy.) 


136 


THE  TISSUES 


k  " 


h 


-.-.  d 


\ 


f 


\ 


outside  the  neurilemma,  a  nucleated  sheath  of  connective-tissue 
origin,  known  as  the  sheath  of  Henle  (Fig.  8i). 

Two  views  as  to  the  relation  of  the 
axolemma  to  the  neurilemma  are  illus- 
trated in  Fig.  80.  According  to  one  the 
neurilemma  is  continuous,  merely  dipping 
into  the  nodes  of  Ranvier,  where  it  touches 
the  axolemma  or  the  axone.  According  to 
the  second  both  neurilemma  and  axolem- 
ma are  interrupted  at  the  node,  but  unite 
with  each  other  there  to  enclose  completely 
the  medullary  substance  of  the  internode. 

According  to  the  views  illustrated  in 
Fig.  82,  that  part  of  the  axone  which  lies 
between  two  nodes  is  enveloped  by  a  cell, 
or  by  several  cells  forming  a  syncytium. 
The  outer  homogeneous  membrane  there 
pictured  would  thus  be  of  the  nature  of  a 
cell  membrane  or  cuticle,  and  would  cor- 
respond to  the  neurilemma.  The  trabeculse 
(protoplasmic  strands  and  neurokeratin 
network,  of  which  some  of  the  larger 
strands  would  represent  the  incisures  of 
Schmidt)  would  correspond  to  the  spongio- 
plasm,  and  just  along  the  outer  side  of  the 
axone  would  constitute  the  axolemma. 
The  myelin  would  thus  be  enclosed  within 
the  cylindrical  neurilemma  ceU  which  sur- 
rounds the  axone. 

Recent  experiments  of  Bethe  and  others 
tend  to  prove  an  interruption  of  the  peri- 
fibrillar substance  at  the  node  of  Ranvier. 
They  consider  the  axone  at  the  node  as 
probably  crossed  by  a  sieve-like  plate, 
through  the  holes  of  which  the  fibrils  pass, 
but  which  completely  interrupts  the  peri- 
fibrillar substance.  The  accuracy  of  these 
observations  has  been  disputed. 

MeduUated  nerve  fibres  vary 
greatly  in  size.  The  finer  fibres  have 
a  diameter  of  from  2  to  4.^,  those 
of  medium  size  from  4  to  lo/Jt,  the 
largest  from  10  to  20/^.  They  have 
few  branches,  and  these  are  always  given  off  at  the  nodes  of  Ranvier. 
(b)  MeduUated  axones  without  a  neurilemma  are  the  medullated 


Fig. 


Fig.  81. 


Fig.  80. — Diagram  of  Structure  of 
a  Medullated  Nerve  Fibre  of  a  Peri- 
pheral Nerve  showing  two  different 
views  (one  on  each  side)  as  to  rela- 
tions of  neurilemma  and  axolemma 
and  their  behavior  at  the  nodes  of 
Ranvier.  (Szymonowicz.)  a,  Neuro- 
fibrils; b,  cement  substance;  c,  axone; 

d,  incisure  of  Schmidt;  e,  nucleus  of 
neurilemma;  /,  meduUary  sheath;  g, 
sheath  of  Schwann;  h,  axone;  i,  axo- 
lemma; y,  sheath  of  Schwann;  h,  node 
of  Ranvier. 

Fig.  81. — Piece  of  Medullated 
Nerve  Fibre  from  Human  Radial 
Nerve.  X400.  Osmic-acid  fixation 
and  stain.  (Szymonowicz.)  a,  Me- 
dullary sheath;  h,  axone;  c,  sheath 
of  Henle;  d,  nuclei  of  Henle's  sheath; 

e,  nucleus  of  neurilemma. 


XERVE  TISSUE 


137 


nerve  fibres  of  the  central  nervous  system  as  described  by  most 
observers.  Cajal,  as  already  mentioned  (p.  135),  describes  these 
fibres  as  having  a  neurilemma.  Their  structure  is  similar  to  the 
above-described  structure  of  a  medullated  nerve  fibre  with  a  neuri- 
lemma, except  for  the  absence  of  the  latter 
sheath. 

As  to  the  physiological  significance  of  the 
structural  elements  of  the  neurone,  we  have  little 
absolute  knowledge  but  certain  fairly  well- 
grounded  theories. 

That  portion  of  the  neurone  which  surrounds 
the  nucleus — the  cell  body — is,  as  already  stated, 
the  genetic  centre  of  the  neurone,  the  nucleus  as 
in  other  cells  being  probably  concerned  in  the 
general  cell  metabolism.  From  the  behavior  of 
the  processes  when  cut  off  from  the  cell  body  it 
is  evident  that  the  latter  is  the  trophic  or  nutritive 
centre  of  the  neurone. 

It  is  probable  that  in  most  or  perhaps  all 
neurones  the  usual  direction  of  conduction  along 
the  axone  is  cellulifugal,  i.e.,  from  cell  body  to 
terminal  arborization.  The  dendrites  and  cell 
body  would  receive  and  probably  integrate  the 
various  nerve  impulses  received  by  the  neurone. 
In  other  words,  the  dendrites  and  cell  body 
receive,  the  axone  transmits  and  the  axone 
branches  and  terminal  arborizations  distribute. 
This  general  direction  of  conduction  indicates  a 
certain  polarity  of  the  neurone.  While  the 
cerebro-spinal   ganglion  cell  is  obviously  polar- 


FiG.  82. — Scheme  of  Structure  of  Medullated  Per- 
ipheral Xerve  Fibre  of  a  Fish  (XemilefF).  A,  Cross 
section;  B,  longitudinal  section;  on  left,  fibre  is  shown 
as  stained  intra  vitam  with  methylene  blue;  on  right, 
myelin  is  shown  black  as  in  osmic  acid  staining,  with 
the  incisures  of  Schmidt  indicated;  sz,  cells  of  sheath 
of  Schwann;  n,  their  nuclei;  ss,  sheath  of  Schwann; 
sp,  processes  of  the  cells  of  sheath  of  Schwann  or  the 
myelin  sheath  network;  Ic,  larger  trabeculx-  of  proto- 
plasmic framework  of  medullarj'  sheath  arranged 
obliquely  to  axis-cylinder  and  forming  the  so-called 
"funnels";  leo,  clear  streaks  in  fibres  treated  with 
osmic  acid,  corresponding  to  le,  incisures  of  .Schmidt; 
mo,  myelin  blackened  with  osmic  acid;  ox,  axis- 
cylinder;  pa,  periaxial  s[)ace  around  axis-cylinder;  gs, 
"coagulum  sheath,"  granules  [irobably  representing 
coagulatcfl  fluid  in  periaxial  s[)a(e;  />/,  peri|)heral, 
non-fibrillar,  part  of  axis-cylinder;  /,  neurofibrils  of 
axis-cylinder;  r,  ring-like  thickening  of  Schwann's 
sheath  at  node  of  Ranvier;  o,  cavity  in  r. 


138  THE  TISSUES 

ized,  yet  if  its  peripheral  process  be  regarded  as  an  axone,  the  latter  would 
evidently  constitute  an  exception  to  conduction  along  the  axone  being  ceUu- 
lifugal.  There  are  cases  {e.g.,  unipolar  cerebro-spinal  ganglion  cell)  where  the 
nervous  impulse  may  apparently  pass  from  one  process  to  another  without 
traversing  the  body  of  the  cell. 

Regarding  the  chrom.ophilic  substance,  certain  facts,  such  for  example  as 
the  entire  absence  of  chromophilic  bodies  in  many  nerve  cells,  which  nevertheless 
undoubtedly  functionate;  the  absence  of  these  bodies  in  all  axones;  the  diminu- 
tion of  the  chromatic  substance  during  functional  activity;  its  much  greater 
diminution  if  activity  be  carried  to  the  point  of  exhaustion;  these  together  with 
its  behavior  under  certain  pathological  conditions,  all  favor  the  theory  that  the 
stainable  substance  of  Nissl  is  not  the  active  nerve  element  of  the  cell,  but  is 
rather  of  the  nature  of  a  nutritive  element. 

There  thus  remains  to  be  considered  as  possible  factors  in  the  transmission 
of  the  nervous  impulse  the  neurofibrils  and  the  perifibrillar  substance.  While  a 
few  investigators  are  inclined  to  magnify  the  importance  of  the  latter,  the  ma- 
jority agree  in  considering  the  neurofibrils  as  the  principal  conducting  mechanism 
of  the  neurone.  The  already  referred  to  observations  of  Bethe  regarding  the 
interruption  of  the  perifibrillar  substance  at  the  constricted  portion  of  the  axone 
and  at  the  nodes  of  Ranvier,  would,  if  true,  be  obviously  in  favor  of  this  view. 
It  is  also  obvious  that  if  the  neurofibrils  are  the  sole  conducting  substance  and 
if  they  do  not  anastomose  within  the  body  of  the  vertebrate  neurone,  we  would 
be  driven  to  conclude  there  must  be  an  extracellular  anastomosis.  The  proba- 
bility, however,  is  rather  against  both  of  these  premises.  The  neurofibrils  are 
probably  a  differentiation  of  the  spongioplasm,  while  the  perifibrillar  substance 
and  chromophilic  bodies  are  specializations  of  the  hyaloplasm. 

As  to  the  manner  in  which  neurones  are  connected,  there  are  two  main  the- 
ories, the  contact  theory  and  the  continuity  theory. 

According  to  the  contact  theory  each  neurone  is  a  distinct  and  separate  entity. 
Association  between  neurones  is  by  contact  or  contiguity  of  the  terminals  of  the 
axone  of  one  neurone  with  the  cell  body  or  dendrites  of  another  neurone,  and 
never  by  continuity  of  their  protoplasm.  This  theory,  which  is  known  as  the 
"neurone  theory"  and  which  received  general  acceptance  as  a  result  of  the  work 
of  Golgi,  His,  Forel,  Cajal,  and  others,  has  been  recently  called  in  question  by 
such  prominent  neurologists  as  Apathy,  Bethe,  Held,  and  Nissl,  on  the  ground 
that  in  some  cases  the  neurofibrils  are  continuous  throughout  a  series  of  neurones. 
The  point  of  contact  between  two  neurones  is  called  a  synapsis  (Fig.  83),  and 
the  conception  that  there  is  some  kind  of  interruption  or  discontinuity  in  neural 
circuits  involving  more  than  one  neurone  has  proved  useful  to  physiologists.  It 
affords  an  explanation  of  certain  differences  between  conduction  through  a  cir- 
cuit of  two  or  more  neurones  and  conduction  through  a  nerve  fibre  alone.  For 
example,  an  impulse  takes  longer  to  traverse  the  circuit  than  to  traverse  a  nerve 
fibre  of  equal  length.  Also  a  stimulus  may  pass  in  either  direction  along  a  nerve 
fibre,  but  cannot  be  "reversed"  along  a  circuit.  Based  upon  the  contact  theory 
is  the  so-called  "retraction  hypothesis,"  which  held  that  a  neurone  being  asso- 
ciated with  other  neurones  only  by  contact  was  able  to  retract  its  terminals, 
thus  breaking  the  association  and  throwing  itself,  as  it  were,  out  of  circuit. 


NERVE  TISSUE 


139 


According  to  the  continuity  theory,  while  the  perifibrillar  substance  is  inter- 
rupted as  above  described,  the  neurofibrils,  are  continuous.  According  to 
this  theory  the  neurofibrils,  which  form  a  plexus  or  network  within  the  cell 
body  and  dendrites,  are  connected  with  a  pericellular  netivork — the  Golgi  net 
— which  closely  invests  the  cell  body  and  its  dendrites.  Externally  the  Golgi 
net  is  further  connected  with  the  neurofibrils  of  the  axones  and  collaterals 
of  other  nerve  cells.  This  connection  is  either  direct,  or,  as  some  believe,  through 
another  general  (diffuse)  extracellular  network.     The  neurofibrils  are  thus,  accord- 


FiG.  83.— yl,  B,  C,  Three  cells  of  the  Ventral  Cochlear  Nucleus  of  Rabbit,  showing 
terminals  of  fibres  of  the  cochlear  nerve  and  their  relations  to  the  cell  bodies  (Cajal). 
a,  a,  a,  Fibres  of  the  cochlear  nerve,  which  break  up  into  terminal  ari^orizations  upon  the 
cells;  b,  c,  terminal  rings.  The  i>oints  of  contact  between  the  terminals  of  the  axone  of 
one  neurone  and  the  cell  bodv  and  dendrites  of  the  other  neurone  constitute  a  "synapsis." 


ing  to  this  theory,  continuous  and  form  two  or  possibly  three  continuous  net- 
works: (a)  an  intracellular  network,  (b)  a  pericellular  network  (Golgi),  and  (c) 
a  more  diffuse  extracellular  network,  lying  between  the  cells.  The  existence  of 
(c)  is  extremely  doubtful  and  it  seems  probable  that  the  Golgi  network  is  either 
non-nervous  or  an  artefact.  Thus  the  main  point  at  issue  is  whether  the 
neurofibrils,  in  such  pericellular  terminals  as  are  illustrated  in  Fig.  83,  are  con- 
tinuous with  the  neurofibrils  within  the  cell  enveloped  or  are  separate  from  the 
latter. 

The  individuality  of  the  ncun;ne  and  the  interdef)cndence  of  its  various  parts 
arc  strikingly  shown  by  its  behavior  when  injured.  'I'hat  degenerative  changes, 
which  progress  to  complete  flisappearance  of  the  nerve  structures,  take  place  in 


140 


THE  TISSUES 


the  distal  part  of  a  nerve  when  that  nerve  is  cut  across  has  long  been  accepted 
as  one  of  the  fundamental  laws  of  neuropathology  (law  of  Wallerian  degenera- 
tion). In  terms  of  the  neurone  concept  this  would  mean  that  an  axone  cut  off 
from  its  cell  of  origin  degenerates  and  disappears  and  this  behavior  of  the  axone 
would  accord  with  the  already  stated  fact  that  the  cell  body  is  the  trophic  center 
of  the  neurone.  The  degenerative  changes  in  the  axone  are  best  shown  in  their 
earlier  stages  by  an  osmic  acid  (p.  7)  or  by  a  Marchi  (p.  34)  stain.  Later, 
when  the  degenerated  fibres  have  been  largely  replaced  by  connective  tissue,  the 
Weigert  method  is  most  satisfactory,  especially  in  the  central  nervous  system. 
In  this  case,  of  course,  the  degeneration  is  indicated  by  an  absence  of  stain,  while 
in  the  Marchi  method  a  positive  picture  of  the  degenerating  myelin  sheaths  is 


B 


C 


Fig.  84. — A,  Normal  Nerve  Fibres  from  Sciatic  Nerve  of  Rabbit,  osmic  acid  fixa- 
tion and  stain;  each  fibre  shows  node  of  Ranvier.  B,  Two  fibres  from  distal  part  of 
rabbit's  sciatic  five  days  after  cutting  the  nerve;  shows  segmentation  of  myelin;  C,  three 
fibres  from  distal  part  of  rabbit's  sciatic  three  weeks  after  cutting  nerve;  most  of  the 
myelin  has  been  absorbed  and  only  traces  of  the  axones  remain. 


seen.  When  the  nerve  is  cut  the  first  changes  affect  the  cut  ends  and  seem  to  be 
of  a  traumatic  character  such  as  formation  of  bulbous  enlargements  of  the  ends 
of  the  axones,  increase  and  separation  of  neurofibrils  and  formation  of  sprouts. 
This  phase  is  soon  passed  over  in  the  distal  stump,  while  in  the  central  it  may  pass 
over  into  a  beginning  regeneration  of  the  nerve  fibres.  In  the  distal  portion  a 
degeneration  of  the  nerve  fibres  throughout  their  length  and  including  their  termi- 
nal arborization  now  takes  place.  All  parts  of  the  nerve  fibre  are  affected.  In 
the  medullary  sheath  the  changes  consist  in  segmentation  of  the  sheath,  break- 
ing up  of  the  segments  into  granules  and  finally  complete  absorption  (Fig.  84). 
While  undergoing  these  physical  changes  chemical  changes  are  also  taking  place 
in  the  myelin  which  result  in  its  breaking  down  into  simpler  fatty  substances 
which  give  the  fat  reaction  to  the  Marchi  stain.  At  the  same  time  the  neuro- 
fibrils become  irregular  and  granular  and  the  axis-cylinders  finally  disappear. 


XERVE  TISSUE 


141 


The  neurilemma  cells  of  the  peripheral  nerve  fibres  are  peculiar  in  that  they  do 
not  degenerate;  instead  of  this  their  protoplasm  increases,  and  their  nuclei  pro- 
liferate. These  cells  are  apparently  concerned  in  the  disintegration  and  absorp-. 
tion  of  the  myelin.  They  also  form  protoplasmic  bands  which  play  an  important 
part  in  the  regeneration  of  the  nerve  (see  below).  The  same  rule  holds  good  for 
dendrites  as  for  axones  as  far  as  it  has  been  possible  to  determine,  namely,  that 
cut  oflf  from  their  cells  of  origin  they  undergo  complete  degeneration. 

At  the  time  the  law  of  Wallerian  degeneration  was  established  it  was  believed 
that  the  central  portion  of  the  nerve  and  the  cell  bodies  remained  intact  after 
division  of  the  nerve.     More  recently  the  method  of  Marchi  (for  nerve  fibres)  and 


Fig.  85. — Two  ]M(jtor  Cells  from  Ventral  Horn  of  Dorsal  Cord  of  Rabbit;  fifteen 
days  after  cutting  major  sacro-sciatic  nerve.  A,  Cell  in  which  the  chromophilic  bodies 
appear  disintegrate.!  and  nucleus  eccentric;  B,  cell  showing  more  advanced  chromatoly- 
sis,  the  chromophilic  substance  being  present  only  in  the  dendrites  and  around  the 
nucleus  in  the  form  of  a  homogeneous  mass;  nucleus  causes  bulging  of  surface  of  cell. 


the  method  of  Nissl  (for  neurone  bodies)  have  shown  marked  degenerative 
changes  in  the  parts  proximal  to  the  lesion.  The  extent  and  rapidity  of  these 
changes  are  dependent  mainly  upon  three  factors  (i)  the  type  of  neurone — some 
neurones  being  apparently  more  resistant  than  others  to  injury;  (2)  the 
character  of  the  injury — e.g.,  tearing  the  nerve  causing  the  greatest  reaction; 
cutting  the  nerve,  a  reaction  of  less  intensity;  pinching  the  nerve,  the  least  degree 
of  reaction;  and  (3)  the  location  of  the  injury,  an  injury  near  the  cell  body  caus- 
ing more  effect  centrally  than  one  at  a  distance,  in  other  words,  the  effect  de- 
I)ends  upon  the  fjerccntage  of  the  neurone  cut  ofT.  If  the  injury  is  very  near  the 
cell  body  the  latter  may  ultimately  disappear,  the  proximal  portion  of  the  nerve 
fibre  which  remains  attached  to  it  undergoing  a  final  degeneration  similar  to 
that  of  the  distal  severed  portion.     In  the  cell  body  there  is  an  initial  turgescence^ 


142  THE  TISSUES 

followed  by  disintegration  and  disappearance  of  the  chromophilic  bodies  begin- 
ning near  the  centre  of  the  cell,  and  a  displacement  of  the  nucleus  toward  the 
periphery.  This  reaction  on  the  part  of  the  cell  body  to  injury  to  its  axone — 
"central  chromatolysis "  and  "nuclear  eccentricity" — is  sufi&ciently  characteristic 
to  have  led  to  the  designation  "axonal  degeneration"  (Fig.  85). 

If  the  neurone  body  survive  the  injury  regeneration  takes  place.  This  con- 
sists in  a  reappearance  of  the  chromophilic  substance,  beginning  near  the  nucleus, 
a  return  of  the  nucleus  to  its  normal  position,  and  a  slow  subsidence  of  the  tur- 
gescence.  While  this  is  going  on  the  axones  of  the  central  stump  grow  across 
the  scar  to  the  protoplasmic  bands  beyond  formed  by  the  neurilemma  cells  of  the 
peripheral  stump,  and  find  their  way  along  or  in  them  to  their  former  termina- 
tions. According  to  some  authorities  the  neurilemma  cells  can  do  more  than 
this  and  form,  in  young  animals  at  least,  new  nerve  fibres  which,  however,  do  not 
persist  unless  they  form  connections  with  the  central  stump.  The  outgrowth 
(centrogenetic)  theory  seems  more  probable  than  the  latter  (autogenetic)  theory. 

A  B 


Fig.   86. — A,  Neuroglia  Cell — Spider  Type — Human  Cerebrum.     B,   Neuroglia  CeU 
— Mossy  Type — Human  Cerebrum. 

The  rapidity  of  the  above  degenerative  and  regenerative  changes  varies 
according  to  the  metabolic  activity  of  the  animal,  i.e.,  they  are  much  more  rapid 
in  warm-blooded  than  in  cold-blooded  animals,  and  in  summer  than  during 
hibernation.     They  are  also  influenced  by  the  age  of  the  animal. 

The  importance  of  these  degenerations  from  the  standpoint  of  anatomy  lies 
in  the  fact  that,  by  using  such  methods  as  Nissl,  Weigert,  and  Marchi,  one  is 
enabled  to  trace  the  connections  between  cell  bodies  and  nerve  fibres  throughout 
the  nervous  system. 

Neuroglia 

This  is  a  peculiar  form  of  connective  tissue  found  only  in  the 
nervous  system.  Unlike  the  other  connective  tissues,  neurogha 
is  of  ectodermic  origin,  being  developed  from  the  ectodermic  cells 
which  line  the  embryonic  neural  canal.  These  cells,  at  first  mor- 
phologically identical,  soon  differentiate  into  neuroblasts  or  future 


XERVE  TISSUE 


143 


neurones,  and  spongioblasts  or  future  neuroglia  cells,  the  latter  most 
probably  being  in  the  form  of  a  syncytium.  Later  this  syncytium 
differentiates  fibres,  the  neuroglia  fibres,  which,  according  to  Weigert 
and  others,  may  be  entirely  separate  from  the  cells  (Fig.  87),  but 
more  probably  lie  wholly  or  at  least  partly  within  them.  In  the 
syncytium  there  are  also  to  be  distinguished  an  endoplasm  of  granular 
protoplasm  and  a  clear  ectoplasm  which  may  perhaps  be  regarded 
as  a  matrix.  (See  also  Fig.  313.)  The  structure  of  neuroglia  would 
thus  be  analogous  to  that  of  fibrous  connective  tissue,  i.e.,  composed 


Fig.  87. — Neuroglia  Cells  and  Fibres  from  the  White  Matter  of  the  Human  Cere- 
bellum stained  by  Weigert's  neuroglia  stain.  A,  Neuroglia  cell;  B,  blood-vessel  cut 
longitudinally,  and  C,  blood-vessel  cut  transversely,  showing  enveloping  neuroglia 
fibres;  a,  neuroglia  fibres;  b,  cytoplasm  of  neuroglia  cell.     (Cajal.) 


of  cells,  the  neuroglia  cells,  a  fibrillar  substance,  the  neuroglia  fibres, 
and  a  ground  substance.  The  Golgi  method  apparently  reveals  a 
great  variety  of  neurogha  cells  which  may  be  divided  into  cells  with 
straight  radiating  unbranched  processes,  spider  cells,  and  rough 
thick  branching  cells,  mossy  cells.  It  seems  probable  that  in  the 
former  both  cells  and  fibres  are  stained  while  in  the  latter  only  por- 
tions of  the  cells  or  syncytium,  this  method  not  differentiating 
between  cells  and  fibres. 

An  increased  activity  of  the  neuroglia,  due  it  may  be  to  some 
pathological  cause,  is  indicated  by  increase  in  the  endoplasm,  by 
proliferation  of  the  nuclei,  and  by  some  cells  detaching  themselves 


144  THE  TISSUES 

from  the  syncytium  and  becoming  amoeboid.  Such  amoeboid  cells 
may  convey  various  products  of  degeneration  to  the  vicinity  of  the 
perivascular  lymph  spaces.  There  may  also  result  a  temporary  in- 
crease in  the  ghal  fibres  (ghosis). 

According  to  good  authorities  a  continuous  glial  membrane  forms 
the  outer  boundary  of  the  ectodermal  elements  of  the  central  nervous 
system,  i.e.,  the  nerve  tissue  and  glia.  This  glial  membrane  is  of 
course  in  apposition  with  the  mesodermic  connective  tissue  which 
forms  the  pia  or  inner  covering  of  the  brain  and  cord  and  also  with 
the  connective  tissue  of  the  adventitia  of  the  blood-vessels  which 
penetrate  the  central  nervous  system.  The  ghal  membrane  is 
formed  by  superficial  flattened  cells  and  processes  of  other  glial  cells 
which  come  into  contact  with  the  connective  tissues.  The  lining 
of  the  cavity  of  the  neural  tube  is  formed  by  the  ependymal  cells 
which  are  a  form  of  neuroglia  cells.  These  cells  are  columnar  epi- 
thelial cells  each  with  a  process  penetrating  a  variable  distance  into 
the  wall  of  the  neural  tube  and  joining  the  general  neurogha  syncy- 
tium. Their  nuclei  lie  near  the  central  cavity  of  the  tube  and  they 
contain  glia  fibres.  The  inner  lining  of  the  chorioid  plexuses  of  the 
brain  is  a  single  layer  of  cuboidal  epithelial  cells  which  have  prob- 
ably a  secretory  function  and  contribute  to  the  production  of  the 
cerebro-spinal  fluid.  It  is  probable  that  the  ependyma  cells  also 
have  a  secretory  activity. 

It  is  probable  that  the  neurilemma  cells  also  originate  from  the 
neural  tube.  If  this  is  the  case  it  is  evident  that  they  may  be 
regarded  as  a  special  form  of  neuroglia  cells.  It  has  already  been 
seen  that  in  pathological  changes  they  behave  similarly  to  the 
neuroglia  cells  in  the  central  nervous  system. 

TECHNIC 

(i)  Pieces  of  the  cerebral  cortex  are  stained  by  one  of  the  Golgi  methods. 
If  the  rapid  or  mixed  silver  method  is  used,  sections  must  be  mounted  in  hard  bal- 
sam without  a  cover;  if  the  slow  silver  or  the  bichlorid  method  is  used,  the  sec- 
tions may  be  covered.  Sections  are  cut  from  75  to  loo/^  in  thickness,  cleared  in 
carbol-xylol  or  oil  of  origanum  and  mounted  in  balsam.  This  section  shows  only 
the  external  morphology  of  the  neurone.  It  is  also  to  be  used  for  studying  the 
different  varieties  of  neuroglia  cells  as  demonstrated  by  Golgi's  method  (see 
page  143). 

(2)  Thin  transverse  slices  from  one  of  the  enlargements  of  the  spinal  cord 
are  fixed  in  absolute  alcohol.  Thin  sections  (5  to  lo/*)  are  stained  by  Nissl's 
method  (page  38)<-and  mounted  in  balsam.     This  section  is  for  the  purpose  of 


NERVE  TISSUE  145 

studying  the  internal  structure  of  the  nerve  cell  and  processes  as  demonstrated  by 
the  method  of  Xissl. 

(3)  MeduUated  Xerve  Fibres  (fresh). — Place  a  small  piece  of  one  of  the  sciatic 
or  lumbar  nerves  of  a  recently  killed  frog  in  a  drop  of  salt  solution  and  tease  lon- 
gitudinally. Cover  and  examine  as  quickly  as  possible.  Note  the  diameter  of 
the  axone  and  of  the  medullary  sheath  and  the  appearance  of  the  nodes  of  Ran- 
vier.     An  occasional  neurilemma  nucleus  can  be  distinguished. 

(4)  Medullated  nerve  fibres — fibres  from  the  cauda  equina  (this  material  has 
the  advantage  of  being  comparatively  free  from  fibrous  connective  tissue) — are 
fixed  in  formalin-Muller's  fluid  (technic  5,  p.  7),  and  hardened  in  alcohol.  Small 
strands  are  stained  twenty  minutes  in  strong  picro-acid-fuchsin  solution  (technic 
2,  p.  20),  washed  thoroughly  in  strong  alcohol,  cleared  in  oil  of  origanum,  thor- 
oughly teased  longitudinally  and  mounted  in  balsam. 

General  References  for  Further  Study  of  Tissues 

Barker:  The  Nervous  System. 

Bethe:  Allgemeine  .^natomie  und  Physiologic  des  Nervensystem. 
Cabot:  A  Guide  to  the  Clinical  Examination  of  the  Blood  for  Diagnostic 
Purposes. 

Ewing:  Clinical  Pathology  of  the  Blood. 

Hertwig:  Die  Zelle  und  die  Gewebe. 

Kolliker:  Handbuch  der  Gewebelehre. 

Prenant,  Bouin  et  Maillard:  Traite  d'Histologie. 

Ranvier:  Traite  Technique  d'Histologie. 

Van  Gehuchten:  Le  Systeme  nerveux  de  I'homme. 

Wood:  Laboratory  Guide  to  Clinical  Pathology. 


10 


PART  IV 
THE  ORGANS 


A  tissue  such  as  any  one  of  those  described  in  the  precechng  chap- 
ters scarcely  exists  in  the  pure  state,  that  is  alone  by  itself,  in  the  adult 
body.  Two  or  more  tissues  are  always  associated  and  such  an  associa- 
tion of  two  or  more  tissues  for  the  purpose  of  performing  a  definite 
function  constitutes  an  organ . 

In  practically  all  cases  one  of  the  tissues  is  connective  tissue,  the 
main  function  of  which  is  to  form  a  supportive  framework  for  the 
more  active  specific  tissue  of  the  organ.  In  many  cases  this  connec- 
tive tissue  forms  a  definite  covering  or  capsule.  From  the  capsule 
strands  of  connective  tissue  frequently  extend  down  into  the  organ 
which  branch  and  form  its  connective  tissue  framework.  Sometimes 
the  subdivision  of  the  organ  by  connective  tissue  is  quite  regular 
macroscopic  subdivisions  being  marked  off  by  coarse  connective 
tissue  septa,  and  these  again  subdivided  by  liner  septa.  In  such 
case  the  former  are  known  as  lobes,  the  smaller  as  lobules. 

But  while  an  organ  has  been  defined  as  consisting  of  two  or  more  tis- 
sues and  while  in  general  one  of  these  tissues  is  connective  tissue  frame- 
work and  the  other  the  specific  functioning  tissue  of  the  organ,  such  a 
simple  combination  of  two  tissues  does  not  actually  exist,  for  all  organs 
are  suppHed  with  blood  and  lymph  which  are  distributed  to  them  and 
through  them  b>^  the  blood  and  lymph  vessels.  There  are  thus  car- 
ried into  the  organs  not  only  the  blood  and  lymph  themselves,  but 
also  the  tissues  which  compose  the  walls  of  the  blood  and  lymph 
vessels.  Also  every  organ  has  its  nerve  supply;  thus  nerve  tissue  is 
distributed  through  all  organs. 

Many  organs  are  hollow  tubes  and  the  study  is  the  study  of  the 
structure  of  the  walls  of  the  tube,  such,  e.g.,  are  the  stomach  and 
intestines,  the  heart  and  the  blood-vessels,  the  trachea  and  bronchi. 
Other  organs  not  so  apparently  tubular  still  show  their  tubular  struc- 
ture on  closer  analysis,  such,  e.g.,  are  the  lungs  and  the  duct  glands. 

As  an  organ  has  a  specific  function  and  as  this  function  is  performed 
mainly  by  the  si)ecinc  cells  of  the  organ,  these  cells  show  variations 
in  structure  dependent  ujK)n  whether  the  organ  is  at  vvork  or  at  rest. 

Many  adult  organs  are  so  com[)lex  that  it  is  i)ossible  to  understand 

them  only  by  reference  to  their  development  from  more    simple 

structures. 

1 1<) 


150  THE  ORGANS 

From  the  foregoing  it  follows  that  in  studying  an  organ  there  are 
to  be  considered  primarily: 

(i)  The  specific  tissue  of  the  organ. 

(2)  The  connective  tissue  framework. 

(3)  The  blood  supply. 

(4)  The  nerve  supply. 

(5)  Function. 

(6)  Development. 


CHAPTER  I 

THE  CIRCULATORY  SYSTEM 

The  circulatory  apparatus  consists  of  two  systems  of  tubular 
structures,  the  blood-vessel  system  and  the  lymph-vessel  system, 
which  serve,  respectively,  for  the  transmission  of  blood  and  lymph. 

THE  BLOOD-VESSEL  SYSTEM 

This  consists  of  (a)  a  central  propelling  organ,  the  heart;  (b)  a  series 
of  efferent  tubules — the  arteries — which  by  branching  constantly 
increase  in  number  and  decrease  in  calibre,  and  which  serve  to  carry 
the  blood  from  the  heart  to  the  tissues;  (c)  minute  anastomosing 
tubules — the  capillaries- — into  which  the  arteries  empty  and  through 
the  walls  of  which  the  interchange  of  elements  between  the  blood 
and  the  other  tissues  takes  place;  (^)  a  system  of  converging  tubules 
— the  veins — which  receive  the  blood  from  the  capillaries,  decrease 
in  number  and  increase  in  size  as  they  approach  the  heart,  and  serve 
for  the  return  of  the  blood  to  that  organ. 

The  entire  system — heart,  arteries,  veins,  capillaries — has  a  com- 
mon and  continuous  Hning,  which  consists  of  a  single  layer  of  endothe- 
lial cells.  Of  the  capillaries  this  single  layer  of  cells  forms  the  entire 
wall.  In  the  heart,  arteries,  and  veins,  the  endothelium  serves 
simply  as  the  Hning  for  walls  of  muscle  and  connective  tissue. 

Capillaries 

It  is  convenient  to  describe  these  first  on  account  of  their  simplicity 
of  structure.  A  capillary  is  a  small  vessel  from  4.5  to  i6,«  in  diameter. 
Its  wall  consists  of  a  single  layer  of  endothelial  cells.  The  cells  are 
somewhat  elongated  in  the  long  axis  of  the  vessel.  The  smaller  the 
caUbre  of  the  capillary  the  more  elongated  are  the  cells.  Two  endo- 
thelial cells  suffice  to  complete  the  circumference  of  the  smaller 
capillaries,  while  the  larger  requires  three  or  four.  The  protoplasm 
of  the  cells  is  clear  or  finely  granular.  The  nuclei  are  oval,  with 
their  long  axes  in  the  long  axis  of  the  vessel.     In  fixed  material  the 

1.51 


152  THE  ORGANS 

nuclei  bulge  into  the  lumen.  In  the  living  condition  the  lining  of  the 
capillary  is  probably  nearly  smooth.  According  to  some  investiga- 
tors a  deUcate  cuticle  limits  the  cytoplasm  on  the  side  toward  the 
lumen.  The  edges  of  the  cells  are  serrated  and  are  united  by  a  small 
amount  of  intercellular  substance  (p.  77),  which  can  be  demonstrated 
by  the  silver  nitrate  stain.  ^  In  certain  capillaries — those  of  the  early 
embryo,  of  the  kidney  glomeruli,  of  the  chorioid  coat  of  the  eye,  of 
the  liver — no  cell  boundaries  can  be  made  out.  In  these  capillaries 
the  endothelium  appears  to  be  of  the  nature  of  a  syncytium  (p.  68). 
Capillaries  branch  without  diminution  in  calibre,  and  these  branches 


Fig.  88. — ^Large  and  Small  Capillaries.     Silver-nitrate  and  hematoxylin  stain  (technic 
7,  p.  79),  to  show  outlines  of  endothelial  cells  and  their  nuclei. 


anastomose  to  form  capillary  networks,  the  meshes  of  which  differ 
in  size  and  shape  in  different  tissues  and  organs  (Figs.  88,  89,  90). 
The  largest  meshed  capillary  networks  are  found  in  the  serous  mem- 
branes and  in  the  muscles,  while  the  smallest  are  found  in  the  glands, 
as,  e.g.,  the  liver.  As  to  calibre,  the  largest  are  found  in  the  liver, 
the  smallest  in  muscles. 

In  such  thin  membranous  parts  as  the  web  of  the  frog's  foot,  or  the  wall  of 
the  frog's  bladder,  the  blood  may  be  observed  as  it  flows  through  the  arteries,^ 
capillaries,  and  veins.  The  current  is  seen  to  be  fastest  in  the  arteries,  and 
faster  in  the  centre  of  the  vessel  than  at  its  periphery.  It  is  slower  in  the  veins 
and  slowest  in  the  capillaries.  In  the  case  of  the  frog's  bladder,  the  mere  expo- 
sure to  the  air  acts  as  a  sufficient  irritant  to  cause  slight  inflammatory  changes, 
and  the  leucocytes  may  be  seen  adhering  to  the  walls  of  the  capillaries  and 
passing  through  them  into  the  tissues.  The  capillary,  both  from  the  thinness  of 
its  wall  and  from  the  slowness  with  which  the  blood  passes  through  it,  is  peculiarly 
adapted  for  the  interchange  of  material  between  the  blood  and  the  tissues,  and 
it  is  probable  that  it  is  in  the  capillary  that  all  such  interchange  takes  place. 

^  Some  authors  describe  delicate  protoplasmic  anastomoses  between  the  cells  and 
describe  an  irregular  precipitation  of  the  silver  nitrate  corresponding  to  the  spaces  be- 
tween the  anastomosing  threads-  These  spaces  are  interpreted  as  intercellular  channels 
through  which  the  leucocytes  and  plasma  can  pass.  Intracellular  spaces  reacting  to 
silver  nitrate  and  supposed  to  have  a  similar  function  have  also  been  described. 


THE  CIRCLTLATORY  SYSTEM 


153 


Arteries 

The  wall  of  an  artery  consists  of  three  coats: 
(i)  An  inner  coat,  the  intima. 

(2)  The  middle  coat,  the  media. 

(3)  An  outer  coat,  the  advent  ilia. 

The  intima  consists  of  a  single  layer  of  endothelial  cells,  continu- 
ous with  and  similar  to  that  forming  the  walls  of  the  capillaries,  or, 


fed 

Fig.  89. — Diagram  of  Capillaries  and  Small  Artery  showing  their  structure  and 
relations,  a.  Capillaries;  /;,  nuclei  of  ca[)illary  endothelium;  c,  precapillary  arteries;  d, 
arteriole;  e,  large  capillary;/,  small  artery. 

in  arteries  of  considerable  size,  of  this  layer  plus  more  or  less  Qonnec- 
tive  tissue.  The  middle  coat  consists  mainly  of  smooth  muscle,  the 
outer  of  connective  tissue. 

The  structure  of  these  three  coats  varies  according  to  the  size  of 
the  artery,  and  while  the  transition  between  them  is  never  abruj)t,  it 
is  convenient,  for  purposes  of  description,  to  distinguish  (a)  small 
arteries,  (b)  medium  sized  arteries,  and  (c)  large  arteries. 

Small  Arteries.- — Pas.sing  from  a  cajnllary  to  an  artery,  the  first 
change  is  the  addition  of  a  thin  sheath  of  connective  tissue,  the  fibres 


154 


THE  ORGANS 


of  which  are  disposed  longitudinally,  around  the  outside  of  the  endo- 
thelial tube.  A  little  farther  back  isolated  smooth  muscle  cells, 
circularly  arranged,  begin  to  appear  between  the  endothelium  and 
the  connective  tissue.  Such  an  artery  is  known  as  a  precapillary 
artery.  The  next  transition  is  the  completion  of  the  muscular  coat, 
the  muscle  cells  now  forming  a  continuous  layer.  Such  an  artery, 
consisting  of  three  distinct  coats,  the  middle  coat  composed  of  a  single 
continuous  layer  of  smooth  muscle  cells,  is  known  as  an  arteriole  (Fig. 
89,  d;  Fig.  90,  h). 

Medium-sized  Arteries. — This  group   comprises   all   the  named 
arteries  of  the  body  with  the  exception  of  the  aorta  and  the  pulmo- 


FiG.  90. — Capillary  Network  from  Human  Pia  Mater,  showing  also  an  arteriole  in 
"  optical  section"  and  a  small  vein.  X3S0.  (Technic  i,  p.  160.)  a,  Vein;  b,  arteriole; 
c,  large  capillary;  d,  small  capillaries. 


nary.  Their  walls  are  formed  of  the  same  three  coats  found  in  the 
arteriole,  but  the  structure  of  these  coats  is  more  elaborate. 

I.  The  INTIMA  consists  of  three  layers  (Fig.  91). 

{a)  An  inner  endothelial  layer  already  described. 

(h)  A  middle  layer,  the  intermediary  layer  of  the  intima.  This 
is  composed  of  delicate  white  and  elastic  fibrils  which  run  longi- 
tudinally, and  connective-tissue  cells. 

(c)  An  outer  layer,  the  elastic  layer  of  the  intima,  or  membrana 
elastica  interna — a  thin  fenestrated  membrane  of  elastic  tissue.  This 
membrane  is  intimately  connected  with  the  media  and  marks  the 
boundary  between  the  latter  and  the  intima.     In  the  smallest  of 


THE  CIRCLTLATORY  SYSTEM 


155 


the  medium-sized  arteries  the  intermediary  layer  is  often  wanting, 
the  endothelial  cells  resting  directly  upon  the  elastic  membrane. 
Owing  to  the  extensive  amount  of  elastic  tissue  in  their  walls,  there 
is  a  postmortem  contraction  of  arteries  which  results  in  the  intima 
being  thrown  up  into  folds.  For  this  reason  the  elastic  membrane 
presents,  in  transverse  sections  of  an  artery,  the  appearance  of  a 
wa\y  band  (Fig.  91). 


Fig.  91. — From  Cross-section  through  Walls  of  Medium-sized  Artery  and  its 
.'\ccompanying  Vein.  Xys.  (Technics,  p.  160.)  yl,  Intima  of  artery;  a,  its  endothe- 
lial layer;  b,  its  intermediary  layer;  c,  its  elastic  layer;  B,  media  of  artery;  C,  adv-entitia, 
the  upper  part  belonging  to  the  artery,  the  lower  to  the  vein;  within  the  adventitia  are 
seen  the  vasa  vasorum;  D,  media  of  vein;  E,  intima  of  vein;  i,  its  intermediary  layer; 
j,  its  endothelial  layer. 

2.  The  MEDIA  is  a  thick  coat  of  circularly  disposed  smooth  muscle 
cells  (Fig.  gi,B).  Its  thickness  depends  largely  upon  the  size  of  the 
vessel,  though  varying  somewhat  for  different  vessels  of  the  same  size. 
A  small  amount  of  fibrillar  connective  tissue  supports  the  muscle  cells. 
Elastic  tissue  is  present  in  the  media,  the  amount  being  usually  pro- 
portionate to  the  size  of  the  vessel.  In  the  smaller  of  the  medium- 
sized  arteries,  the  elastic  tissue  is  disposed  as  delicate  fibrils  among 
the  muscle  cells.  In  lafger  arteries  many  coarse  fibres  are  intermin- 
gled with  the  fine  fibrils.  When  much  elastic  tissue  is  present  the 
muscle  cells  are  separated  into  more  or  less  well-defined  groups.  In 
such  large  arteries  as  the  subclavian  and  the  carotid,  elastic  tissue 


156 


THE  ORGANS 


occurs  not  only  as  fibrils  but  also  as  circularly  disposed  plates  or 
fenestrated  mem.br anes. 

3.  The  ADVENTiTiA  (Fig.  91,  C)  is  composed  of  loose  fibrous 
connective  tissje  with  some  elastic  fibres.  Occasionally  there  are 
scattered  smooth  muscle  cells.  Both  smooth  muscle  cells  and 
elastic  fibres  are  arranged  longitudinally.  The  adventitia  does  not 
form  a  definitely  outlined  coat  like  the  media  or  intima,  but  blends 


^^ 

■4 

~^&>^^^--^'&- 


/f --------- 


Fig.  92. — From  Transverse  Section  of  Dog's  Aorta.     X60.     (Technic  4,  p.   160.)     a, 
Intima;  h,  media;  c,  adventitia;  d,  vasa  vasorum;  e,  elastic  tissue;/,  endothelium. 

externally  with  the  tissues  surrounding  the  artery  and  serves  to 
attach  the  artery  to  these  tissues.  In  some  of  the  larger  arteries 
the  elastic  tissue  of  the  adventitia  forms  an  especially  well-defined 
layer  at  the  outer  margin  of  the  media.  This  is  known  as  the 
membrana  elastica  externa.  In  general,  it  may  be  said  that  the 
thickness  of  the  adventitia  and  the  amount  of  elastic  tissue  present 
are  directly  proportionate  to  the  size  of  the  artery. 

Large  arteries  like  the  aorta  (Fig.  92)  have  the  same  three  coats 
as  small  and  medium-sized  arteries.  The  layers  are  not,  however,  so 
distinct.     This  is  due  mainly  to  the  excessive  amount  of  elastic 


THE  CIRCULATORY  SYSTEM 


157 


tissue  in  the  media  (Fig.  93),  which  makes  indistinct  the  boundaries 
between  intima  and  media,  and  between  media  and  adventitia.  The 
walls  of  the  aorta  are  thin  in  proportion  to  the  size  of  the  vessel,  in- 
creased strength  being  obtained  by  the  decided  increase  in  the  amount 
of  elastic  tissue.  Of  the  intima,  the  endothelial  cells  are  short  and 
polygonal;  the  intermediary  layer  similar  to  that  of  a  medium-sized 
artery;  the  elastic  layer  less  distinct  and  often  broken  up  into  several 


Fig.  93.— From  Transverse  Section  of  Dog's  Aorla,  lo  show  Elastic  Tissue 
X60.  rrechnic  7,  p.  160.)  Elastic  tissue  stained  black,  a,  Intima;  b,  media;  c, 
adventitia. 

thin  layers.  The  media  consists  mainly  of  elastic  tissue  arranged 
in  circular  plates  or  fenestrated  membranes.  Between  the  elastic- 
tissue  plates  are  groups  of  smooth  muscle  cells  and  some  fibrillated 
connective  tissue.  The  adventitia  resembles  that  of  the  medium-sized 
artery.     There  is  no  external  elastic  membrane. 

Certain  arlerics  have  structural  peculiarities.  The  arteries  of  the  brain  and 
cord  are  thin-walled  in  proportion  to  their  calibre,  the  inner  elastic  membrane 
is  especially  well  defined,  and  there  are  few  elastic  fibres  in  the  media.  In  the 
renal,  crjeliac,  mesenteric,  and  external  iliac  arteries  there  is  little  or  no  connective 


158  TH-E  ORGANS 

tissue  separating  the  endothelium  from  the  media.  In  the  subclavian,  the  media 
contains  longitudinal  muscle  cells.  Longitudinally  running  muscle  cells  occur 
in  the  adventitia  of  the  umbilical  arteries,  in  the  iliac,  splenic,  renal,  superior 
mesenteric  and  dorsahs  penis.  The  radial,  femoral  and  coeliac  arteries  have 
comparatively  little  elastic  tissue,  while  in  the  common  iliac,  carotid,  and  axillary 
the  elastic  tissue  is  in  excess  of  the  muscular. 

Veins 

The  walls  of  veins  resemble  those  of  arteries.  There  are  the 
same  three  coats,  intima,  media,  and  adventitia,  and  the  same  elements 
enter  into  the  structure  of  each  coat  (Fig.  91).  Venous  walls  are  not, 
however,  so  thick  as  those  of  arteries  of  the  same  calibre,  and  the 
coats  are  not  so  distinctly  differentiated  from  one  another.  The 
transition  from  capillary  through  the  precapillary  vein  to  the  small 
vein  is  similar  to  that  described  under  arteries  (page  154).  Unlike 
the  artery,  the  thickness  of  the  wall  of  a  vein  and  its  structure  are 
not  directly  proportionate  to  the  size  of  the  vessel,  but  depend  also 
upon  other  factors  such  as  the  position  of  the  vein  and  the  support 
given  to  its  walls  by  surrounding  structures. 

Of  the  INTIMA  the  endothelial  layer  and  the  intermediary  layer 
are  similar  to  those  of  the  artery.  The  elastic  layer  is  not  always 
present,  is  never  so  distinct,  and  is  not  wavy  as  in  the  artery  (Fig. 
91).  The  result  is  a  lack  of  demarcation  between  intima  and  media, 
the  connective  tissue  of  the  intermediary  layer  of  the  intima  merging 
with  the  mixed  muscle  and  connective  tissue  of  the  media.  Project- 
ing at  intervals  from  the  inner  surface  of  the  wall  of  some  veins  are 
valves.  These  are  derived  entirely  from  intima  and  consist  of  loose 
fibrous  and  elastic  tissue  covered  by  a  single  layer  of  endothelium. 
Valves  are  especially  large  and  strong  in  the  larger  veins  of  the  lower 
limbs.  They  are  absent  in  the  veins  of  the  brain  and  cord  and  their 
membranes,  in  the  veins  of  bones,  in  the  umbilical  vein,  and  in  most 
of  the  visceral  veins  with  the  exception  of  some  branches  of  the 
portal. 

The  MEDIA  of  veins  is  thin  as  compared  with  that  of  arteries  of 
the  same  size.  It  consists  of  fibrous  and  elastic  tissue  and  smooth 
muscle  cells.  The  amount  of  muscle  is  comparatively  small  and  the 
cells  are  arranged  in  groups  through  the  connective  tissue. 

The  ADVENTITIA  is  well  developed  in  proportion  to  the  media. 
It  consists  of  mixed  fibrous  and  elastic  tissue  and  usually  contains 
along  its  inner  margin  small  bundles  of  longitudinally  disposed 
smooth  muscle  cells. 


THE  CIRCULATORY  SYSTEM  159 

The  media  is  thickest  in  the  veins  of  the  lower  extremities, 
especially  the  popliteal,  and  in  the  veins  of  the  skin.  In  the  veins 
of  the  head  and  abdomen  the  media  is  very  thin,  while  in  the  sub- 
clavian and  superior  vena  cava  and  in  the  veins  of  bones,  of  the  pia 
mater,  dura  mater,  and  retina,  there  is  an  almost  entire  absence  of 
media. 

Arteries  are  as  a  rule  empty  after  death,  while  veins  contain  blood. 
The  absence  of  much  elastic  tissue  in  the  walls  of  the  veins  prevents 
any  such  extensive  post-mortem  contraction  as  occurs  in  the  arteries. 
Veins  tend  to  collapse  after  death,  but  are  usually  prevented  from 
doing  so  by  the  presence  of  blood  in  them. 

In  the  iliac  and  femoral  veins,  longitudinally  disposed  muscle  occurs  in  the 
inner  part  of  the  media.  The  umbUical  vein,  like  the  corresponding  artery,  has 
three  distinct  muscular  coats.  Longitudinal  muscle  fibres  are  present  in  the 
adventitia  of  the  superior  vena  cava  (hepatic  and  abdominal  portion)  and  of 
the  portal  and  hepatic  veins.  In  the  upper  portion  of  the  inferior  vena  cava, 
in  the  superior  vena  cava,  the  jugular,  innominate,  and  subclavian,  there  is  little 
muscle  tissue  in  any  of  the  coats,  while  in  the  veins  of  the  brain  and  its  mem- 
branes, the  retina,  the  placenta  and  the  bones,  no  muscle  is  present. 

Vasa  Vasorum. — Medium  and  large  arteries  and  veins  are  sup- 
plied mth  small  nutrient  vessels — vasa  vasorum.  These  vessels  run 
in  the  adventitia,  small  branches  penetrating  the  media  (Figs.  91 
and  92). 

Lymph  channels  are  found  on  the  outer  surface  of  many  blood- 
vessels. Some  of  the  smaller  vessels  are  surrounded  by  spaces  Hned 
by  endothehum — perivascular  lymph  spaces.  These  communicate 
with  the  general  lymphatic  system. 

Nerves.— The  walls  of  the  blood-vessels  are  supplied  with  both 
medullated  and  non-mcdullated  fibres.  The  latter  are  axones  of 
sympathetic  neurones.  As  these  nerves  control  the  calibre  of  the 
vessels  they  are  known  as  vasomotor  nerves.  They  form  plexuses 
in  the  adventitia,  from  which  are  given  off  branches  which  pene- 
trate the  media  and  terminate  on  the  muscle  cells.  The  medul- 
lated fibres  are  the  peripheral  arms  of  spinal  or  cranial  ganglion  cells. 
The  larger  fibres  run  in  the  connective  tissue  outside  the  adventitia. 
From  these  are  given  off  branches  which  enter  the  media,  divide  re- 
peatedly, lose  their  medullary  sheaths,  and  terminate  mainly  in  the 
media,  although  some  fibres  have  been  tracerl  to  their  terminations  in 
the  intima. 


160  THE  ORGANS 

TECHNIC 

(i)  Capillaries,  Arterioles,  Small  Arteries,  and  Veins.— Fix  an  entire  brain, 
or  slices  about  an  inch  thick  from  its  surface,  in  formalin-Miiller's  fluid  for  twenty- 
four  hours  (technic  5,  p.  7).  Remove  the  pia  mater,  especially  the  thinner  parts 
which  He  in  the  sulci  between  the  convolutions,  and  harden  in  graded  alcohols. 
Select  a  thin  piece,  stain  with  haematoxylin  (lightly)  and  eosin  (strongly)  (technic 
I,  p.  20),  and  mount  in  balsam  or  in  eosin-glycerin.  The  veins,  having  thin 
walls  and  being  usually  well  filled  with  blood,  appear  distinct  and  red  from  the 
eosin-stained  red  cells.  The  arteries,  having  thicker  walls,  in  which  are  many 
hemoglobin-stained  nuclei,  have  a  rather  purple  color.  Between  the  larger 
vessels  can  be  seen  a  network  of  anastomosing  capillaries  with  their  thin  walls 
and  bulging  nuclei.  Some  are  filled  with  blood  ceUs;  others  are  empty  with 
their  collapsed  walls  in  apposition.  Note  the  appearance  of  an  arteriole,  first 
focusing  on  its  upper  surface,  then  focusing  down  through  the  vessel.  In  this 
way  what  is  known  as  an  "optical  section"  is  obtained,  the  artery  appearing 
as  if  cut  longitudinally.  Trace  the  transition  from  arteriole  to  precapillary 
artery  and  the  breaking  up  of  the  latter  into  the  capillary  network.  Similarly 
follow  the  convergence  of  capillaries  to  form  a  small  vein. 

(2)  Instructive  pictures  of  the  relations  of  arteries,  capillaries,  and  veins  in 
living  tissues  may  be  obtained  by  curarizing  a  frog,  distending  the  bladder  with 
normal  saline  introduced  through  a  small  catheter  or  cannula,  opening  the  abdo- 
men and  drawing  out  the  bladder,  which  can  then  be  arranged  upon  the  stage 
of  the  microscope.  The  passage  of  the  blood  from  the  arteries  through  the 
capillary  network  and  into  the  veins  is  beautifully  demonstrated. 

(3)  For  studying  the  structure  of  the  walls  of  a  medium-sized  artery  and  vein 
remove  a  portion  of  the  radial  artery,  or  other  artery  of  similar  size,  and  its  accom- 
panying vein,  together  with  some  of  the  surrounding  tissues.  Suspend  the  ves- 
sels, with  a  small  weight  attached,  in  formalin-Miiller's  fluid  (technic  5,  p.  7). 
Sections  should  be  cut  transversely,  stained  with  haematoxylin-eosin  (technic 
I,  p.  20),  or  with  haematoxylin-picro-acid  fuchsin  (technic  3,  p.  21),  and 
mounted  in  balsam.  The  vessels  of  the  adventitia — vasa  vasorum — are  con- 
venient for  studying  the  structure  of  arterioles  and  small  veins. 

(4)  Fix  a  piece  of  aorta  in  formalin-Miiller's  fluid,  care  being  taken  not  to 
touch  the  delicate  endothelial  lining.  Stain  transverse  sections  with  haema- 
toxylin-eosin or  with  haematoxylin-picro-acid  fuchsin  and  mount  in  balsam. 

(5)  The  outlines  of  the  lining  endothelial  cells  may  be  demonstrated  as  fol- 
lows: Kill  a  small  animal,  cut  the  aorta,  insert  a  glass  cannula  and,  under  low 
pressure,  thoroughly  wash  out  the  entire  vascular  system  with  distilled  water. 
Follow  the  water  by  a  one-per-cent.  aqueous  solution  of  silver  nitrate.  Remove 
some  of  the  smaller  vessels,  split  longitudinally,  mount  in  glycerin,  and  expose 
to  the  direct  sunlight.  After  the  specimen  has  turned  brown  examine  with  the 
low  power.     The  outlines  of  the  cells  should  appear  brown  or  black. 

(6)  The  endothelium  of  the  smaller  vessels  and  capillaries  may  also  be  demon- 
strated in  the  specimen  described  under  technic  8,  p.  79. 

(7)  The  elastic  tissue  of  the  blood-vessels  is  best  demonstrated  by  means  of 
Weigert's  elastic-tissue  stain.  Prepare  sections  of  medium-sized  vessels  and  of 
the  aorta,  as  above  described  (3),  and  stain  as  in  technic  3,  p.  28. 


THE  CIRCULATORY  SYSTEM  161 

The  Heart 

The  heart  is  a  part  of  the  blood-vessel  system  especially  differ- 
entiated for  the  purpose  of  propelHng  the  blood  through  the  vessels. 

The  main  mass  of  the  heart  wall  consists  of  a  special  form  of 
muscle  tissue  already  described  as  heart  muscle  (page  119).  This 
constitutes  the  myocardium.  On  its  inner  and  outer  sides  the  myo- 
cardium is  covered  by  connective-tissue  membranes  Uned,  respect- 
ively, with  endotheUum  and  mesotheHum  and  known  as  the  endo- 
cardium  and  epicardium. 

The  MYOCARDIUM  varies  in  thickness  in  different  parts  of  the 
heart,  being  thickest  in  the  left  ventricle,  thinnest  in  the  auricles. 
A  ring  of  dense  connective  tissue,  the  auriculo-ventricular  ring,  com- 
pletely separates  the  muscle  of  the  auricles  from  that  of  the  ventri- 
cles, except  in  the  median  septum  where  the  auricular  and  ventricu- 
lar muscle  is  continuous.  The  auricular  muscle  consists  of  an  outer 
coat  common  to  both  auricles,  the  fibres  of  which  have  a  transverse 
or  somewhat  obHque  direction,  and  of  an  inner  coat,  independent  for 
each  auricle,  the  fibres  of  which  are  longitudinally  disposed.  Bun- 
dles of  these  fibres  stand  out  as  ridges  along  the  inside  of  the  auricles. 
They  are  more  strongly  developed  in  the  right  than  in  the  left  auricle. 
Between  the  two  coats  bundles  of  muscle  fibres  are  frequently  found 
which  run  in  various  directions. 

The  disposition  of  the  muscle  tissue  of  the  ventricles  is  much  more 
compHcated.  It  is  usually  described  as  composed  of  several  layers, 
the  fibres  of  which  run  in  different  directions.  The  meaning  of 
these  fibre  layers  becomes  apparent  when  we  study  the  arrangement 
of  the  fibres  in  embryonic  hearts  in  which  the  connective  tissue  has 
been  broken  down  by  maceration.  Thus  dissected,  the  muscle  of 
the  ventricles  is  seen  to  consist  mainly  of  two  sets  of  fibres,  a  super- 
ficial set  and  a  deep  set.  These  run  at  approximately  right  angles 
to  each  other.  Both  sets  of  fibres  begin  at  the  auriculo-ventricular 
rings.  The  superficial  fibres  wind  around  both  ventricles  in  a  spiral 
manner,  becoming  constantly  deeper,  to  terminate  in  the  papillary 
muscles  of  the  opposite  ventricle.  The  deeper  fibres  pass  from  the 
auriculo-ventricular  ring  around  the  ventricle  of  the  same  side, 
through  the  interventricular  septum  and  terminate  in  the  papillary 
muscles  of  the  opposite  ventricle. 

The  ENDOCARDIUM  covcrs  the  inner  surface  of  the  myocardium 
and  forms  the  serous  lining  of  all  the  chambers  of  the  heart.  M. 
11 


162  THE  ORGANS 

the  arterial  and  venous  orifices  it  is  seen  to  be  continuous  with  and 
similar  in  structure  to  the  intima  of  the  vessels.  It  consists  of  two 
layers:  (a)  an  inner  composed  of  a  single  layer  of  endotheHal  cells, 
corresponding  to  the  endothelial  lining  of  the  blood-vessels;  and  (b) 
an  outer  composed  of  mixed  fibrous  and  elastic  tissue  and  smooth 
muscle  cells.  Externally  the  endocardium  is  closely  attached  to  the 
myocardium. 

Strong  fibrous  rings  (annuli  fibrosi),  composed  of  mixed  fibrous 
and  elastic  tissue,  surround  the  openings  between  auricles  and 
ventricles.  Similar  but  more  delicate  rings  encircle  the  openings 
from  the  heart  into  the  blood-vessels. 

The  heart  valves  are  attached  at  their  bases  to  the  annuli  fibrosi. 
They  are  folds  of  the  endocardium,  and  like  the  latter  consist  of 
fibrous  and  elastic  tissue  continuous  with  that  of  the  rings  and 
covered  by  a  layer  of  endothelium. 

The  EPiCARDiUM  is  the  visceral  layer  of  the  pericardium.  It  is 
a  serous  membrane  like  the  endocardium,  which  it  resembles  in 
structure.  It  consists  of  a  layer  of  mixed  fibrous  and  elastic  tissue 
covered  over  by  a  single  layer  of  mesothelial  cells.  Beneath  the 
epicardium  there  is  usually  more  or  less  fat. 

Blood-vessels. — Blood  for  the  nutrition  of  the  heart  is  supplied 
through  the  coronary  arteries.  The  larger  branches  run  in  the  con- 
nective tissue  which  separates  the  bundles  of  muscle  fibres.  From 
these,  smaller  branches  pass  in  among  the  individual  fibres,  where 
they  break  up  into  a  rich  capillary  network  with  elongated  meshes. 
From  the  myocardium,  capillaries  penetrate  the  connective  tissue 
of  the  epicardium  and  endocardium.  The  auriculo-ventricular 
valves  are  supplied  with  blood-vessels,  while  in  the  semilunar  valves 
blood-vessels  are  wanting. 

Lymphatics. — ^Lymph  channels  traverse  the  epicardium  and 
endocardium  and  enter  the  valves.  Within  the  myocardium 
minute  lymph  vessels  have  been  demonstrated  between  the  muscle 
fibres  and  accompanying  the  blood-vessels. 

Nerves- — These  are  derived  from  both  cerebro-spinal  (vagus) 
and  sympathetic  systems  (cervical  gangha)  and  consist  of  both 
medullated  and  non-meduUated  fibres.  Sympathetic  gangHon  cells 
are  distributed  in  groups  throughout  the  myocardium,  the  largest, 
lying  in  the  epicardium  near  the  base  of  the  heart,  being  known  as 
the  cardiac  ganglion  or  ganglion  of  Wrisberg.  Among  these  cells 
the  nerve  fibres  form  plexuses  from  which  both  motor  and  sensory 


THE  CIRCULATORY  SYSTEM  163 

terminals  are  given  off  to  the  muscle.     (For  nerve  endings  in  heart 
muscle  see  page  440.) 

TECHNIC 

(i)  The  Heart. — Cut  pieces  through  the  entire  thickness  of  the  wall  of  one 
of  the  ventricles,  care  being  taken  not  to  touch  either  the  serous  surface  or  the 
lining  endothelium.  Fix  in  formalin-Miiller's  fluid  (technic  5,  p.  7).  Cut  trans- 
verse and  longitudinal  sections;  stain  with  haematoxylin-eosin  (technic  i,  p.  20) 
and  mount  in  balsam. 

(2)  Treat  the  entire  heart  of  a  small  animal  (e.g.,  guinea-pig  or  frog)  in 
the  same  manner  as  the  preceding,  making  transverse  sections  through  both 
ventricles. 

(3)  An  entire  heart,  human  or  animal,  may  be  fixed  in  the  distended  condi- 
tion by  filling  with  formalin-Miiller's  fluid  under  low  pressure  and  then  tying  off 
the  vessels.  The  entire  heart  thus  distended  is  placed  in  a  large  quantity  of 
the  same  fixative. 

Developmext  of  the  Circulatory  System 

The  blood-vessels  and  the  heart  begin  their  development  separately  and 
afterward  become  united.  Both  are  derived  from  mesoderm,  but  while  the 
heart  develops  within  the  embryo,  the  earliest  blood-vessels  and  blood  are 
developed  from  extra-embryonic  mesoderm.  The  earliest  vessels  to  be  formed 
are  the  capillaries.  These  make  their  appearance  in  the  mesodermic  tissue 
near  the  periphery  of  the  area  vasculosa  which  surrounds  the  developing  embryo. 
Here  groups  of  cells  known  as  "blood  islands"  differentiate  from  the  rest  of 
the  mesodermic  cells,  appearing  in  the  chick  by  the  end  of  the  first  day  of 
incubation.  The  superficial  cells  of  these  islands  become  flattened  to  form 
the  endothelium,  which  is  at  this  stage  apparently  a  syncytium  through  which 
the  nuclei  are  scattered  and  showing  no  evidences  of  cell  boundaries.  This 
endotheUal  syncytium  surrounds  the  remaining  more  central  cells,  from  which 
blood  cells  are  developed.  These  represent  the  earliest  blood-vessels.  The 
channels,  which  are  at  first  unconnected,  anastomose  and  give  rise  to  a  network 
of  channels  which  are  the  earliest  capillaries.  These  develop  rapidly  in  the 
area  vasculosa  and  some  of  them  increase  in  size  to  become  arteries  and  veins, 
the  smooth  muscle  and  connective  tissue  of  their  walls  being  differentiated 
from  the  surrounding  mesoderm.  These  grow  toward,  and  finally  into,  the 
embryo  where  they  unite  with  the  heart.  In  granulation  tissue,  and  in  new 
growths  in  general,  both  normal  and  pathological,  new  blood-vessels  apparently 
develop  as  off-shoots  from  other  vessels.  These  are  at  first  solid  extensions 
of  endothelium  which  become  hollowed  out.  In  regard  to  the  origin  of  the 
later  vessels  in  the  extraembryonic  area,  and  those  within  the  embryo,  there 
are  two  views:  (i)  that  they  represent  outgrowths  from  the  original  capillaries; 
(2)  that  they  arise  in  silii  in  the  same  manner  as  the  earliest  capillaries  and 
unite  secondarily  to  form  networks.  The  weight  of  evidence  at  present  favors 
the  latter  view.     The  entire  vascular  system  is  at  first  represented  by  a  network 


164 


THE  ORGANS 


of  capillaries.     As  development  proceeds  some  of  the  channels  enlarge  to  form 
the  arteries  and  veins. 

The  heart  first  appears  as  an  endotheUal  tube,  the  primitive  endocardium, 
at  a  very  early  age  of  embryonic  life,  in  the  chick  embryo  during  the  first  day 
of  incubation.  It  apparently  begins  its  rhythmic  contraction  before  any 
contractile  fibrils  can  be  distinguished  in  its  walls  and  before  any  connection 
with  blood-vessels  has  been  estabhshed.  The  origin  of  the  cardiac  endothelium 
is  not  definitely  known.  It  is  believed  by  some  to  be  of  entodermic  origin, 
by  others  of  m.esodermic,  by  still  others  to  be  partly  derived  from  each  of 
these  layers.  Around  this  endothelial  tube,  but  separated  from  it  by  a  space, 
there  develops  from  mesoderm  an  entirely  distinct  muscular  tube,  the  primitiv 


Coelom 


Parietal  mesoderm 


Ectoderm 


i'*^^*.  ^ 


Visceral  mesoderm  Blood  islands 

Fig.  94. — Section  of  Blastoderm  of  Chick  of  42  Hours'  Incubation.  Photograph- 
The  cells  of  the  blood  islands  are  difierentiated  into  nucleated  red  blood  ceUs  (erythro. 
blasts)  and  the  endothelium  of  the  vessels. 

myocardium.  These  two  tubes  are  at  first  united  only  in  places  by  bands  of 
connective  tissue.  Later  they  unite  so  that  the  inner  tube,  the  endocardiume 
becomes  a  lining  for  the  outer  tube,  the  myocardium.  The  union  of  the  two 
heart  tubes  occurs  very  early.  The  foregoing  description  applies  to  the  chick 
and  to  those  mammals  thus  far  studied.  In  the  earliest  human  embryos 
(2  to  3  mm.)  the  heart  is  already  a  single,  slightly  coiled  tube  connected  at  its 
cephalic  end  with  the  ventral  aorta  and  caudally  with  the  omphalo-mesenteric 
veins.  The  epicardium,  as  the  visceral  layer  of  the  pericardium,  has  a  sepa- 
rate origin,  being  constricted  off  from  that  portion  of  the  mesoderm  which 
hnes  the  primary  body  cavity. 


THE  LYMPH-VESSEL  SYSTEM 

The  larger  lymph  vessels  are  similar  in  structure  to  veins.  Their 
walls  are,  however,  thinner  than  those  of  veins  of  the  same  calibre 
and  they  contain  more  valves.     These  are  folds  of  the  intima,  and 


THE  CIRCULATORY  SYSTEM  165 

always  occur  in  pairs.  They  are  arranged  with  considerable  regu- 
larity and  in  small  vessels  where  the  intima  forms  the  entire  wall 
there  is  a  distinct  bulging  just  above  the  valve  which  gives  the  vessel 
a  quite  characteristic  appearance.  They  are  capable  of  great 
distention,  and  when  empty  collapse  so  that  their  thin  walls  are 
in  apposition. 

The  largest  of  the  lymph  vessels,  the  thoracic  duct,  has  three  well- 
defined  ccats:  an  intima  consisting  of  the  usual  lining  endothelium 
resting  upon  a  subendothelial  layer  of  delicate  fibro-elastic  tissue,  the 
outermost  elastic  fibres  having  a  longitudinal  arrangement;  a  fairly 
thick  media  of  circularly  disposed  smooth  muscle  cells  which  occur  in 
groups  separated  by  connective  tissue  containing  a  few  elastic  fibres 
and  an  advent  it  ia  of  longitudinally  running  connective  tissue  contain- 
ing elastic  fibres  and  strengthened  by  bundles  of  longitudinal  smooth 
muscle. 

Lymph  capillaries  resemble  blood  capillaries  in  that  their  walls 
are  composed  of  a  single  layer  of  endothelial  cells.  The  cells  are 
rather  larger  and  more  irregular  than  in  blood  capillaries,  the  capil- 
laries themselves  are  larger,  and,  instead  of  being  of  uniform  diameter 
throughout,  vary  greatly  in  calibre  within  short  distances.  In  cer- 
tain tissues  dense  networks  of  these  lymph  capillaries  are  found. 
Cleft-like  lymph  spaces — perivascular  lymph  spaces — ^partially  sur- 
round the  walls  of  the  smaller  blood-vessels. 

Lymph  spaces  without  endothelial  or  other  apparent  lining  also 
occur.  Examples  of  these  are  the  pericellular  lymph  spaces  found  in 
various  tissues  and  the  canaliculi  of  the  cornea  and  of  bone  (pages 
83  and  loi). 

Similar  in  character  to  lymph  spaces  are  the  body  cavities,  peri- 
toneal, pleural,  and  pericardial,  with  their  linings  of  serous  membranes. 
These  cavities  first  appear  in  the  embryo  as  a  cleft  in  the  mesoderm 
— the  ccelom,  body  cavity,  or  pleuro peritoneal  cleft.  This  cleft  is  lined 
with  mesothelium  beneath  which  the  stroma  is  formed.  These  mem- 
branes not  only  line  the  cavities,  but  are  reflected  over  most  of  the 
viscera  of  the  abdomen  and  thorax.  They  consist  of  a  stroma  of 
mixed  fibrous  and  elastic  tissue,  covered  on  its  inner  side  by  a  layer 
of  mesothelium,  the  two  being  separated  by  a  homogeneous  basement 
membrane.  The  stroma  contains  numerous  lymphatics.  These 
have  been  described  as  communicating  with  the  free  surfaces  by 
means  of  openings — slomata.  Recent  observations,  however,  would 
seem  to  indicate  that  these  stomata  are  artefacts. 


166  THE  ORGANS 

That  the  lymph-vessels  form  a  definite  and  closed  system  of 
channels  and  are  not  in  direct  communication  with  the  lymph  spaces 
has  been  clearly  demonstrated. 

The  origin  of  the  lymphatic  vessels  is  not  clear.  According  to  some  investi- 
gators they  originate  as  evaginations  from  the  vascular  system,  starting  as  four 
buds,  two  from  the  veins  of  the  neck,  and  two  from  the  veins  in  the  inguinal 
region.  The  two  anterior  buds  appear  first  (pig  embryo  of  14.5  mm.)  and  are  in 
communication  with  the  anterior  cardinal  vein.  A  little  later  the  posterior  buds 
connected  with  the  posterior  cardinals  appear.  From  these  buds  the  entire 
lymphatic  plexus  develops  by  a  process  of  evagination. 

According  to  other  investigators,  the  lymphatic  vessels  first  appear  as  min- 
ute spaces  in  the  mesenchyme  of  the  axilla  and  groin  (during  second  month  in 
human  embryo).  These  spaces  enlarge  and  by  sending  off  branches  give  rise 
to  the  network  of  lymphatic  vessels.  According  to  this  veiw,  the  connection 
between  lymphatic  vessels  and  veins  is  secondary. 

TECHNIC 

(i)  Remove  a  portion  of  the  central  tendon  of  a  rabbit's  diaphragm.  Rub 
the  pleural  surface  gently  with  the  finger  or  with  a  brush  to  remove  the  mesothe- 
lium.  Rinse  in  distilled  water  and  treat  with  silver  nitrate  as  in  technic  7,  p.  79. 
Mount  in  glycerin.  If  the  silver  impregnation  is  successful,  the  networks  of 
coarser  and  finer  lymphatics  can  be  seen  as  well  as  the  outlines  of  the  endothelium 
of  their  walls.  If  care  has  been  taken  not  to  touch  the  peritoneal  surface,  the 
peritoneal  mesothelium  and  the  stomata  are  frequently  seen. 

(2)  The  Thoracic  Duct. — Remove  a  portion  of  the  thoracic  duct,  fix  in  forma- 
lin-Muller's  fluid  (technic  5,  p.  7),  and  stain  sections  with  haematoxylin-eosin 
(technic  i,  p.  20). 

General  References  for  Further  Study  of  the  Circulatory  System 

KoUiker:  Handbuch  der  Gewebelehre  des  Menschen,  vol.  iii. 
Stohr:  Text-book  of  Histology. 

Schafer:  Histology  and  Micros,copic  Anatomy,  in  Quain's  Elements  of  Anat- 
omy, tenth  edition. 


CHAPTER  II 
LYMPHATIC  ORGANS 

Lymphatic  Tissue^ 

So-called  lymphatic  tissue  consists  of  reticular  connective  tissue 
and  a  special  type  of  cells,  lymphoid  cells,  which  fill  in  the  meshes  of 
the  reticulum.  Lymphoid  cells  are  small  spheroidal  cells,  each  hav- 
ing a  single  nucleus  which  almost  completely  fills  the  cell.  Lym- 
phatic tissue  may  be  diffuse  or  circumscribed.  In  diffuse  lymphatic 
tissue  the  cells  are  not  closely  packed  and  there  is  no  distinct  de- 
marcation between  the  lymphatic  and  the  surrounding  tissues.  An 
example  of  diffuse  lymphatic  tissue  is  seen  in  the  stroma  of  the 
mucous  membrane  of  the  gastro-intestinal  canal.  In  circumscribed 
lymphatic  tissue  the  cells  are  very  closely  packed,  often  completely 
obscuring  the  reticulum.  There  is  also  a  quite  distinct  demarca- 
tion between  the  lymphatic  and  the  surrounding  tissues.  Such  a 
circumscribed  mass  of  lymphatic  tissue  is  known  as  a  lymph  nodule. 

The  Lymph  Nodes 

Lymph  nodes  are  small  bodies,  usually  oval  or  bean-shaped,  which 
are  distributed  along  the  course  of  the  lymph  vessels.  In  some 
regions  they  are  arranged  in  series  forming  "chains"  of  lymph 
nodes  as,  e.g.,  the  axillary  and  inguinal. 

Each  lymph  node  is  surrounded  by  a  capsule  of  connective  tissue 
which  sends  trabeculcB  or  septa  into  the  organ.  The  capsule  and  septa 
constitute  the  connective-tissue  framework  of  the  node,  and  serve  as  a 
support  for  the  lymphatic  tissue  (Fig.  95). 

The  capsule  is  composed  of  fibrous  connective  tissue.  Toward 
the  surface  of  the  capsule  the  fibres  are  loosely  arranged  and  there 
are  comparatively  few  elastic  fibres.     This  outer  layer  of  the  capsule 

'In  the  preceding  editions  "  lymphatic  tissue"  was  placed  according  to  name  rather 
than  structure  among  the  tissues.  As  it  consists  of  a  connective  tissue  framework  suj)- 
porting  a  special  type  of  cell  which  has  a  specific  function,  it  is  more  properly  classi- 
fied as  an  organ.  On  account  of  the  peculiar  structure  and  wide  dislril)ulion  of  the 
"tissue"  and  on  account  of  convenience  and  long  usage,  the  term  "  lym[)hatic  tissue" 
is  still  retained. 

1G7 


168  THE  ORGANS 

blends  with  the  surrounding  tissues  and  serves,  Hke  the  fibres  of  the 
arterial  adventitia,  to  attach  the  organ  to  them.  The  inner  layer 
of  the  capsule  consists  of  a  more  dense  connective  tissue,  is  richer  in 
elastic  fibres,  and  contains  some  smooth  muscle  cells.  At  one  point, 
known  as  the  hilum  (Fig.  95),  there  is  a  depression  where  the  con- 
nective tissue  of  the  capsule  extends  deep  into  the  substance  of  the 
node.  This  serves  as  the  point  of  entrance  for  the  main  arteries 
and  nerves,  and  of  exit  for  the  veins  and  efferent  lymph  vessels. 


h  g  f 

Fig.  95. — Section  through  Entire  Human  Lymph  Node,  including  Hilum.  XiS. 
(Technic  i,  p.  172.)  Dark  zone,  cortex;  light  central  area,  medulla,  a,  Lymph  nodule 
of  cortex;  b,  germinal  centres;  c,  trabeculse  containing  blood-vessels;  d,  capsule;  e, 
hilum;  /,  lymph  sinus  of  medulla;  g,  lymph  cords  of  medulla;  h,  lymph  sinuses  of 
medulla  and  cortex. 

The  connective-tissue  septa,  which  extend  from  the  capsule  into 
the  interior  of  the  node  incompletely  divide  it  into  irregular  inter- 
communicating compartments.  In  the  peripheral  portion  of  the 
node  these  compartments  are  somewhat  spheroidal  or  pear-shaped. 
Toward  the  centre  of  the  node  the  septa  branch  and  anastomose 
freely,  with  the  result  that  the  compartments  are  here  narrower, 
more  irregular,  and  less  well  defined. 

Within  the  compartments  formed  by  the  capsule  and  the  septa  is 
the  lymphatic  tissue.  Near  the  capsule  where  the  compartments 
are  large  and  spheroidal  or  pear-shaped,  the  lymphatic  tissue  is 
arranged  in  masses  which  correspond  in  shape  to  the  compartments. 


LYMPHATIC  ORGANS 


169 


These  are  known  as  lymph  nodules  (Fig.  95).  In  the  centre  of 
each  nodule  is  usually  an  area  in  which  the  cells  are  larger,  are  not 
so  closely  packed,  and  show  marked  mitosis.  As  it  is  here  that 
active  proliferation  of  lymphoid  cells  takes  place,  this  area  is  known 
as  the  germinal  centre  (Figs.  95  and  96).  Immediately  surrounding 
the  germinal  centre  is  a  zone  in  which  the  lymphoid  cells  are  more 
closely  packed  than  elsewhere  in  the  nodule  (Fig.  96).  This  is 
apparently  due  to  the  active  production  of  new  cells  at  the  germinal 
centre  and  the  consequent  pushing  outward  of  the  surrounding 
cells.  In  stained  sections  the  centre  of  the  nodule  is  thus  lightly 
stained,  while  immediately  surrounding  this  light  area  is  the  darkest 


Fig.  96. — Section  through  Cortex  and  Portion  of  Medulla  of  Human  Lymph  Node 
(Technic  2,  p.  172.)  a,  Capsule;  h,  lymph  sinus;  c,  trabecula;  d,  closely  packed  cells 
at  outer  border  of  lymph  nodule;  e,  germinal  centre;  /,  lymph  cords  in  medulla. 

portion  of  the  nodule  (Fig.  96).  From  the  inner  sides  of  the  nodules 
strands  of  lymphoid  tissue  extend  into  the  center  of  the  node. 
These  are  known  as  lymph  cords,  and  anastomose  freely.  The 
regular  arrangement  of  the  lymph  nodules  and  trabecular  in  the 
peripheral  portion  of  the  node  contrasts  strongly  with  their  irregu- 
lar arrangement  in  the  centre.  This  determines  a  division  of  the 
nodule  into  two  zones,  an  outer  peripheral  zone  or  cortex  and  a  cen- 
tral zone  or  medulla.  In  both  cortex  and  medulla  the  lymphoid 
tissue  is  always  separated  from  the  cai)sule  or  from  the  septa  by  a 
distinct  space — the  lymph  sinus — which  is  bridged  over  by  reticular 
tissue  containing  comparatively  few  lymphoid  cells  (Fig.  96). 
These  sinuses  form  a  continuous  system  of  anastomosing  channels 
throughout  the  node. 


170  THE  ORGANS 

The  regular  arrangement  of  trabeculse,  and  lymph  nodules  with 
sinuses  between,  which  is  characteristic  of  the  cortex,  makes  this 
part  of  the  organ  easily  understood.  To  appreciate  the  structure  of 
the  medulla  it  must  be  borne  in  mind  that  all  of  these  cortical  struc- 
tures extend  down  into  the  medulla,  the  trabeculas  as  anastomosing 
networks  of  connective  tissue,  the  lymph  nodules  as  cord-Hke  struc- 
tures which  divide  and  anastomose,  the  sinuses  as  more  or  less 
clear  channels  which  always  separate  the  connective  tissue  from  the 
lymph  cords.  These  parts — -trabecula,  sinus,  lymph  cord — all  anas- 
tomosing freely  and  most  irregularly  in  the  medulla,  always  main- 
tain the  same  relation  to  one  another  as  in  the  cortex,  namely, 
that  sinus  is  always  interposed  between  lymph  tissue  and  trabecula. 

The  reticular  connective  tissue  (page  94),  which  forms  a  part  of 
the  lymphatic  tissue  proper,  is  continuous  with  the  fibrous  connec- 
tive-tissue framework  of  the  organ  in  such  a  manner  that  it  is  im- 
possible to  determine  any  demarcation  between  the  two  tissues.  In 
the  lymph  nodules,  and  wherever  the  lymphoid  cells  are  densely 
packed,  the  underlying  reticular  network  is  almost  completely  ob- 
scured. Crossing  the  sinuses,  especially  those  of  the  medulla,  and 
in  specimens  in  which  the  cells  have  been  largely  washed  out  or 
removed  by  maceration,  the  reticular  structure  is  well  shown. 

The  lymphoid  tissue  proper,  as  represented  by  the  lymph  nodules 
and  anastomosing  lymph  cords,  is  thus,  as  it  were,  suspended  in  the 
meshes  of  a  reticulum  which  is  swung  from  the  capsule  and  trabec- 
ulse. As  both  nodules  and  cords  are  everywhere  separated  from  cap- 
sule and  trabeculae  by  the  sinuses,  and  as  these  latter  serve  for  the 
passage  of  lymph  through  the  node,  it  is  seen  that  the  lymphatic  tis- 
sue of  the  node  is  broken  up  in  such  a  manner  as  to  be  bathed  on 
all  sides  by  the  circulating  lymph. 

In  addition  to  the  definitely  formed  lymph  nodes  and  the  well- 
defined  collections  of  lymph  nodules,  such  as  those  of  the  tonsil  or 
of  Peyer's  patches,  small  nodules  or  groups  of  lymphoid  cells  have  a 
wide  distribution  throughout  the  various  organs.  While  many  of 
these  collections  of  lymphatic  tissue  are  inconspicuous,  still  the  ag- 
gregate of  lymph  tissue  thus  distributed  is  by  no  means  inconsider- 
able. The  most  important  will  be  described  in  connection  with  the 
organs  in  which  they  occur. 

Blood-vessels. — Those  which  enter  the  hilum  carry  the  main 
blood  supply  to  the  organ.  Most  of  the  arteries  pass  directly  into 
the  lymphatic  tissue,  where  they  break  up  into  dense  capillary  net- 


LYMPHATIC  ORGAN  171 

works.  Some  of  the  arteries,  instead  of  passing  directly  to  the  lym- 
phatic tissue,  follow  the  septa,  supplying  these  and  the  capsule,  and 
also  sending  branches  to  the  surrounding  lymphatic  tissue.  A  few 
small  vessels  enter  the  capsule  along  the  convexity  of  the  organ  and 
are  distributed  to  the  capsule  and  to  the  larger  septa. 

L5rmphatics. — The  afferent  lymph  vessels  enter  the  node  on  its 
convex  surface  opposite  the  hilum,  penetrate  the  capsule,  and  pour 
their  lymph  into  the  cortical  sinuses.  The  lymph  passes  through  the 
sinuses  of  both  cortex  and  medulla,  and  is  collected  by  the  efferent 

Efferent  lymph,  ves. 


'•'    .     -t -"--,^'''^>i  '  ""iViN        Bloodvessel 
■  Hilus 


-Marginal  sinus 


)^'^^®S;#SW   ••'^-Capsule 

Anereni,       ^.i.^VV  If''  c   ('.tfti-jfe 
lymph,  ves.        \<7%  m,'  r,  .'.  WW*^ 


Afferent 


Fig.  97. — From  a  Section  through  the  Axilla  of  a  Human  Embryo  of  125  mm. 
(4-5  months),  showing  an  Earl}'  Stage  of  a  Lymph  Gland.     (Kling.) 

lymph  vessels  which  leave  the  organ  at  the  hilum.  Within  the  node 
the  lymph  comes  in  contact  with  the  superficial  cells  of  the  nodules 
and  of  the  lymph  cords.  These  cells  are  constantly  passing  out  into 
the  lymph  stream  so  that  the  lymph  leaves  the  node  much  richer  in 
cellular  elements. 

Nerves  are  not  abundant.  Both  medullated  and  non-medullated 
fibres  occur.     Their  exact  modes  of  termination  are  not  known. 

Development. — The  first  indications  of  lymph  node  formation  are  found  in 
the  axilla  and  groin  (pig  embryo  of  about  30  mm.;  human  toward  end  of  third 
month)  in  the  connective  tissue  in  which  the  lymphatic  vessels  arc  best  developed 
(p.  166).  Here  groups  of  more  closely  packed  cells  appear.  As  the  tissue  is  richly 
vascular  it  seems  impossible  to  determine  whether  the  closely  packed  cells 
originate  within  the  blood-vessels  or  develop  from  fixed  connective  tissue  cells. 
Each  group  of  cells  is  the  anlage  of  a  lymph  node  (Fig.  97).  The  immediately 
surrounding  connective  ti.ssuc  forms  the  capsule,  while  the  lymph  channels  just 


172 


THE  ORGANS 


beneath  form  the  subcapsular  or  marginal  sinus  (Fig.  98).  The  point  of  main 
connection  with  outside  blood-vessels  becomes  the  hilum.  As  the  lymph  node 
grows  outward,  parts  of  the  capsule  remain  within  to  form  trabeculas  while  the 
lymph  channels  within  the  nodule  apparently  develop  as  ingrowths  from  the 
marginal  sinus  (Figs.  97  and  98). 


TECHNIC 

(i)  Remove  several  lymph  nodes  from  one  of  the  lower  animals  (ox,  cat,  dog, 
rabbit),  fix  in  formalin-Miiller's  fluid  (technic  5,  p.  7),  and  harden  in  alcohol. 
Cut  thin  sections  through  the  hilum,  stain  with  hasmatoxyUn-eosin  (technic  i,  p. 
20),  or  with  hsematoxylin-picro-acid-fuchsin  (technic  3,  p.  21),  and  mount  in 
balsam. 

Afferent  lymphatic  vessels 


Marginal  sinus 


Capsule 


Dense  lymph, 
tissue 


— Marginal  sinus  (plexus) 
Capsule 
Trabecula 
•Reticular  tissue 


Intermediary 
plexus 


Efferent  lymph,  vessel 


Blood  vessels 


Fig. 


-Diagram  Illustrating  a  Stage  (Later  Than  Fig.  97)  in  the  Development 
of  a  Lymph  Gland.     (Stohr.) 


(2)  Expose  a  chain  of  lymph  nodules  {e.g.,  the  cervical  or  inguinal  of  a  re- 
cently killed  dog  or  cat).  Insert  a  small  cannula  or  needle  into  the  uppermost 
node  and  inject  formalin-Miiller's  fluid  until  the  node  becomes  tense.  By  now 
slightly  increasing  the  pressure  the  fluid  may  be  made  to  pass  into  the  second 
node,  and  so  through  the  entire  chain.  The  nodes  are  then  carefully  dissected  out 
and  placed  for  twenty-four  hours  in  formalin-Miiller's  fluid,  then  hardened  in 
alcohol.  Sections  are  cut  through  the  hilum,  stained  with  haematoxylin-eosin  or 
with  hsematoxylin-picro-acid-fuchsin  and  mounted  in  balsam.  Near  the  centre 
of  the  chain  are  usually  found  nodes  in  which  the  lymph  sinuses  are  properly  dis- 
tended. The  most  proximal  nodes  are  apt  to  be  overdistended,  but  for  this  very 
reason  are  often  excellent  for  the  study  of  the  reticular  tissue  from  which  most 
of  the  ceUs  have  been  washed  out,  especially  in  the  medulla. 

(3)  Human  lymph  nodes  may  be  treated  by  either  of  the  above  methods. 


LYMPHATIC  ORGANS 


173 


Owing  to  the  coalescence  of  their  cortical  nodules  their  structure  is  not  so  easily- 
demonstrated  as  that  of  the  lymph  nodes  of  lower  animals. 


Haemolymph  Nodes 

These  are  lymphoid  structures  which  closely  resemble  ordinary 
lymph  nodes,  but  with  the  essential  difference  that  their  sinuses  are 
hlood  sinuses  instead  of  lymph  sinuses. 

Each  node  is  surrounded  by  a  capsule  of  varying  thickness,  com- 
posed of  fibro-elastic  tissue  and  smooth  muscle  cells.     From  the  cap- 


Fig.  99. — Section  through  Human  Haemolymph  Node,  including  Hilum,  showing  cap- 
sule, trabeculse,  sinuses  filled  with  blood,  and  lymph  nodules.     (Warthin.) 

sule  Iraheciiloe  of  the  same  structure  pass  down  into  the  node,  forming 
its  framework  (Fig.  99).  Beneath  the  capsule  is  a  blood  sinus,  which 
may  be  broad  or  narrow,  and  usually  completely  surrounds  the  node. 
Less  commonly  the  sinus  is  interrupted  by  lymphoid  tissue  extending 
out  to  the  capsule.  From  the  peripheral  sinus  branches  extend  into 
the  interior  of  the  node,  separating  the  lymphoid  tissue  into  cords  or 
islands.  The  relative  proportion  of  sinuses  and  lymphoid  tissue 
varies  greatly,  some  nodes  being  composed  almost  wholly  of  sinuses, 
while  in  others  the  lymphoid  tissue  predominates.  There  is  usually 
a  fairly  distinct  hilum.  In  many  glands  no  differentiation  into 
cortex  and  medulla  can  be  made.     Where  there  arc  a  distinct  medulla 


174 


THE  ORGANS 


and  cortex  the  peripheral  lymphoid  tissue  is  arranged  in  nodules  as  in 
the  ordinary  lymph  node.  Reticular  connective  tissue  crosses  the 
sinuses  and  supports  the  cells  of  the  lymph  nodules  and  cords 
(Fig.  loo). 

The  cellular  character  of  the  lymphoid  tissue  has  led  to  the  sub- 
division of  haemolymph  nodes  into  splenolymph  nodes  and  marrow- 
lymph  nodes.  In  the  splenolymph  node  the  lymphoid  tissue  resembles 
that  of  the  ordinary  lymph  node  of  the  spleen.  In  the  marrow- 
lymph  node,  which  is  the  much  less  common  form,  the  lymphoid 


Vt^-^XSL 


Fig.  ioo. — Section  through  Superficial  Portion  of  Human  Haemolymph  Node 
(Marrowlymph  Node).  (Warthin.)  Capsule,  trabeculse,  and  parts  of  two  adjacent 
nodules;  sinuses  filled  with  blood;  among  the  lymph  cells  are  large  multinuclear 
cells  resembling  those  of  marrow,  nucleated  red  blood  cells,  etc. 


tissue  resembles  red  marrow.  There  are  no  distinct  nodules,  and 
there  is  a  quite  characteristic  distribution  of  small  groups  of  fat  cells. 
The  most  numerous  cells  are  eosinophiles  and  mast  cells  (see  page 
1 06).  Polynuclear  leucocytes  and  large  leucocytes  with  a  single 
lobulated  nucleus  are  less  numerous.  The  very  large  multinuclear 
cells  of  red  marrow  are  also  found,  but  usually  in  small  numbers. 
Large  phagocytes  containing  blood  pigment  and  disintegrating  red 
blood  cells  are  found  in  both  forms  of  haemolymph  nodes,  but  are 
most  numerous  in  the  splenolymph  type.  In  nodes  which  have  a 
brownish  color  when  fresh,  these  phagocytes  frequently  almost  com- 
pletely fill  the  sinuses. 


LYMPHATIC  ORGANS  175 

Further  classification  of  haemolymph  nodes  has  been  attempted, 
but  is  unsatisfactory,  owing  to  the  large  number  of  transitional  forms. 
Thus  many  nodes  are  transitional  in  structure  betwen  the  haemo- 
lymph node  and  the  ordinary  lymph  node,  between  the  splenolymph 
node  and  the  marrowlymph  node,  and  between  the  splenolymph 
node  and  the  spleen. 

Under  normal  conditions  the  h^molymph  nodes  appear  to  be 
concerned  mainly  in  the  destruction  of  red  blood  cells;  possibly  also 
in  the  formation  of  leucocytes.  Under  certain  pathological  con- 
ditions they  probably  become  centres  for  the  formation  of  red  blood 
cells. 

Blood-vessels. — An  artery  or  arteries  enter  the  node  at  the  hilum, 
and  break  up  within  the  node  into  small  branches,  which  communi- 
cate with  the  sinuses  where  the  blood  comes  into  intimate  association 
with  the  lymphoid  tissue.  From  the  sinuses  the  blood  passes  into 
veins,  which  leave  the  organ  either  at  the  hilum  or  at  some  other 
point  on  the  periphery.  The  course  which  the  blood  takes  in  pass- 
ing through  the  haemolymph  node  is  thus  apparently  similar  to  that 
taken  by  the  lymph  in  passing  through  the  ordinary  lymph  node. 

The  relation  of  the  haemolymph  node  to  the  lymphatic  system  is 
not  known,  and  like  ignorance  exists  as  to  its  innervation. 

The  development  of  the  haemolymph  nodes  is  probably  much  the  same  as 
that  of  the  lymph  nodes,  except  for  the  relation  of  the  latter  to  the  lymphatic 
vessels,  the  sinuses  of  the  haemolymph  nodes  being  developed  from  blood-vessels. 

TECHNIC 

Same  as  for  lymph  nodes  (technic  i,  p.  172).  The  nodes  are  found  in  greatest 
numbers  in  the  prevertebral  tissue,  and  are  often  difficult  to  recognize.  Fixing 
the  tissues  in  5-per-cent.  formalin  aids  in  their  recognition  as  it  darkens  the  nodes 
while  bleaching  the  rest  of  the  tissues. 

The  Thymus 

The  thymus  is  an  organ  of  foetal  and  early  extra-uterine  life; 
reaching  in  man  its  greatest  development  at  the  end  of  the  second 
year.  After  this  age  it  undergoes  a  slow  retrograde  change  into  fat 
and  connective  tissue,  until  by  the  twentieth  year  scarcely  a  vestige 
of  glandular  tissue  remains.  The  fully  developed  thymus  presents 
the  following  structure.  The  entire  gland  is  surrounded  by  a  rather 
delicate  and  loose  connective-tissue  capsule  which  attaches  it  to  the 
surrounding  tissues.     From  the  capsule  septa  extend  down  into  the 


176  THE  ORGANS 

organ.     These  branch  and  subdivide  the  gland  into  lobes,  and  these 
into  larger  and  smaller  lobules. 

From  the  perilobular  connective  tissue,  septa  extend  into  the  lobule, 
incompletely  separating  it  into  a  number  of  chambers.  Each  lobule 
.consists  of  a  cortical  portion  and  a  medullary  portion.  The  cortex 
consists  of  nodules  of  compact  lymphatic  tissue,  composed  of  reticular 
tissue  and  lymphoid  cells,  similar  to  those  found  in  the  lymph  node. 
These  occupy  the  chambers  formed  by  the  connective-tissue  septa. 
The  medulla  consists  of  the  same  elements  only  more  loosely  arranged, 


.-_  h 


•*^^ft^> 


c 
Fig.  ioi. — From  Section  of  Human  Thymus,  showing  parts  of  five  lobules  and 
interlobular  septa.     X20.     (Technic,  page  178.)     a,  Cortex;  6,  medulla;  c,  interlobular 
septum. 

the  cells  being  much  less  closely  packed,  thus  forming  a  more  diffuse 
lymphatic  tissue.  There  are  also  in  the  medulla  no  connective-tissue 
septa.  In  some  lobules  the  more  dense  cortical  substance  completely 
encloses  the  medulla.  It  is  common,  however,  for  the  medullary 
tissue  to  extend  to  the  surface  of  a  lobule  at  one  or  more  points  and 
to  be  there  continuous  with  the  medullary  substance  of  an  adjacent 
lobule.  These  interlobular  connecting  strands  of  medullary  substance 
are  known  as  medullary  cords.  In  the  medulla  are  found  a  number 
of  spherical  or  oval  bodies  composed  of  concentrically  arranged  epi- 
thehal  cells.  These  are  known  as  HassalVs  corpuscles  (Fig.  102),  and 
represent  the  only  remains  of  the   original   glandular   epithehum. 


LYMPATHIC  ORGANS  177 

They  are  characteristic  of  the  thymus.     The  central  cells  of  the  cor- 
puscles are  usually  spherical  and  contain  nuclei,  while  the  peripheral 
cells  are  flat  and  non-nucleated.     As  the  entire  corpuscle  takes  a 
bright  red  stain  with  eosin-haematoxylin,  the  corpuscles  stand  out 
sharply  from  the  surrounding  bluish  or  pinkish  lymphatic  tissue. 
With   low   magnifications  they 
are  apt  to  be  mistaken  for  blood- 
vessels. '^''" .  ^.I,.^ 

Unlike  the  other  lymphatic  %^ 

organs,   the  lymph   nodules    of 
the  thymus  contain  no  germinal 

centres.     Mitosis  can,  however,      ;-.-      %  ■' 

usually  be  seen  in  the  lymphoid  ; 

cells.    No  definite  lymph  sinuses  #''^ 

have  been  demonstrated.      Nu-  ......,,,..  v  i^' 

cleated  red  blood  cells  occur  in  ^--m^-^- 

Fig.  I02. — Hassall's  Corpuscle  and  Small 
the  thymus.      The  thymus  must      Portion    of    Surrounding    Tissue.       X6oo. 

therefore  be  considered  one  of     ^^'^  '^""^"''^  ^^^°^-^ 
the  sources  of  lymphoid  cells  and  of  red  blood  cells. 

Blood-vessels. — The  larger  arteries  run  in  the  connective-tissue 
septa.  From  these,  smaller  intralobular  branches  are  given  off, 
which  break  up  into  capillary  networks  in  the  cortex  and  medulla. 
The  capillaries  pass  over  into  veins.  These  converge  to  form  larger 
veins,  which  accompany  the  arteries. 

Of  the  lymphatics  of  the  thymus  little  is  known.  They  appear 
to  originate  in  indefinite  sinuses  within  the  lymphoid  tissue,  whence 
they  pass  to  the  septa  where  they  accompany  the  blood-vessels. 

Nerves. — These  are  distributed  mainly  to  the  walls  of  the  blood- 
vessels. A  few  fine  fibres,  terminating  freely  in  the  lymphatic  tissue 
of  the  cortex  and  of  the  medulla,  have  been  described. 

The  thymus  originates  in  the  entoderm  in  the  region  of  the  third  bran- 
chial groove,  first  as  two  hollow  evaginations  of  the  endothelium  of  the 
pharyngeal  cavity,  which  later  become  solid  cords,  and  then  separate  entirely 
from  the  pharynx.  The  thymus  thus  begins  its  fcetal  existence  as  a  typical 
epithelial  gland.  Into  this  epithelial  structure  mesodermic  cells  grow  and 
difTerentiate  into  lymphatic  tissue.  This  almost  completely  replaces  the  epi- 
thelial tissue,  only  rudiments  of  which  remain  as  Hassall's  corpuscles. 

Stcihr  denies  the  mesodermic  invasion  of  the  thymus  and  consequently  the 
lymphatic  character  of  the  gland.  He  considers  the  specific  cells  of  the  thymus 
as  modified  epithelial  cells  which  have  become  "deceptively  like  lymphoid 
cells."     This  explanation  has  not,  however,  been  generally  accepted. 

12 


178  THE  ORGANS 


TECHNIC 


Fix  the  thymus  of  a  new-born  infant  in  formalin-Miiller's  fluid  (technic  5,  p. 
7),  and  harden  in  alcohol.  Stain  sections  with  h£ematoxylin-eosin  (technic  i, 
p.  20),  or  with  hsematoxylin-picro-acid-fuchsin  (technic  3,  p.  21),  and  mount 
in  balsam. 

The  Tonsils 

The  Palatine  Tonsils  or  True  Tonsils. — These  are  lymphatic 
organs,  essentially  similar  in  structure  to  those  already  described. 


/        d 


^<^ 


Fig.  103. — Vertical  Section  of  Dog's  Tonsil  through  Crypt.  X15.  (Szymonowicz.) 
a,  Lymph  nodule;  b,  epithelium  of  crypt;  c,  blood-vessel;  d,  crypt;  e,  connective-tissue 
capsule;/,  mucous  glands;  g,  epithelium  of  pharynx. 

The  usual  fibrous  capsule  is  present  only  over  the  attached  sur- 
face, where  it  is  firmly  adherent  on  the  one  side  to  the  tonsillar 
tissue  and  on  the  other  to  the  surrounding  structures  from  which  it 
separates  the  tonsils.  From  the  capsule,  connective- tissue  trabecules 
extend  into  the  substance  of  the  organ  and  branch  to  form  its  frame- 
work.    The  free  surface  of  the  tonsil  is  covered  by  a  reflection  of  the 


LYMPHATIC  ORGANS 


179 


stratified  squamous  epithelmm  of  the  pharynx  (Fig.  103) .  This  epithe- 
lium presents  the  same  structure  as  elsewhere  in  the  pharynx,  flat 
surface  cells,  beneath  which  are  irregular  cells,  while  the  deepest  cells 
are  more  or  less  distinctly  columnar.  The  latter  rest  upon  apapillated 
stroma  from  which  they  are  separated  by  ihebasement  membrane.  At 
several  places  on  the  surface  of  the  tonsil  deep  indentations  or  pockets 
occur.  These  are  from  ten  to  twenty  in  number,  are  known  as  the 
crypts  of  the  tonsil  (Fig.  103),  and  are  lined  throughout  by  a  continua- 
tion of  the  surface  epithelium  which  becomes  thinner  as  the  deeper 
part  of  the  crypt  is  reached.  Passing  off  from  the  bottoms  and  sides 
of  the  main  or  primary  crypts  are  frequently  several  secondary 
crypts,  also  lined  with  the  same  type  of  epithelium. 


^'''¥o'-0*, 


fj     v..      (^"a 


Fig.  104. — Vertical  Section  through  Wall  of  Crypt  in  Dog's  Tonsil,  showing  lymphoid 
infiltration  of  epithelium.  Xiso.  (Bohm  and  von  Davidoff.)  o,  Leucocytes  in  epithe- 
lium; b,  space  in  epithelium  filled  with  leucocytes  and  changed  epithelial  cells;  c,  blood- 
vessel; d,  epithelium  beyond  area  of  infiltration;  e,  basal  layer  of  cells. 


The  stroma  consists  of  diffuse  lymphatic  tissue  in  which  are  found 
nodules  of  compact  lymphatic  tissue  similar  to  those  in  the  lymph 
node.  Each  nodule  has  a  germ  centre,  where  active  mitosis  is  going 
on,  and  a  surrounding  zone  of  more  densely  packed  cells.  The  nod- 
ules may  have  a  fairly  definite  arrangement,  forming  a  single  layer 
beneath  the  epithelium  of  the  crypts  or  may  be  arranged  quite  irregu- 
larly, several  nodules  uniting  to  form  masses  of  dense  lymphatic 
tissue.  At  various  points  on  the  surface  of  the  tonsil,  and  especially 
in  the  crypts,  occurs  what  is  known  as  lymphoid  infiltration  of  the 
epithelium  (Tig.  104).  This  consists  in  an  invasion  of  the  epithelium 
by  the  underlying  lymphoid  cells.  It  varies  from  the  presence  of 
only  a  few  lymphoid  cells  scattered  among  the  epithelium,  to  an  almost 


180  THE  ORGANS 

complete  replacement  of  epithelial  by  lymphoid  tissue.  In  this  way 
the  latter  reaches  the  surface  and  lymphoid  cells  are  discharged  upon 
the  surface  of  the  tonsil  and  into  the  crypts.  These  cells  probably 
form  the  bulk  of  the  so-called  salivary  corpuscles.  In  the  connective 
tissue  adjacent  to  the  tonsil  are  numerous  mucous  glands,  the  ducts 
of  which  empty  into  the  tonsillar  crypts. 

The  Lingual  Tonsils — ^Folliculi  Linguales. — These  are  small 
lymphatic  organs  situated  on  the  dorsum  and  sides  of  the  back  part 
of  the  tongue  between  the  circumvallate  papillae  and  the  epiglottis. 
They  are  similar  in  structure  to  the  true  tonsils.  Each  Ungual 
tonsil  has  usually  one  rather  wide-mouthed  deep  crypt  {Xh^  foramen 
cacum  lingucE)  which  may  be  branched  and  which  is  lined  with  a 
continuation  of  the  surface  stratified  squamous  epithelium.  Into 
these  crypts  frequently  open  the  ducts  of  some  of  the  mucous  glands 
of  the  tongue. 

The  Pharyngeal  Tonsils.^ — These  are  lymphatic  structures  which 
he  in  the  naso-pharynx.  They  resemble  the  lingual  tonsils,  except 
that  they  are,  as  a  rule,  not  so  sharply  circumscribed.  Hypertrophy 
of  the  pharyngeal  tonsils,  with  consequent  obstruction  of  the  nasal 
openings,  is  common  especially  in  children,  constituting  what  are 
known  as  adenoids. 

The  blood-vessels  have  a  distribution  similar  to  those  of  the 
lymph  nodes,  but  enter  the  organ  along  its  entire  attached  side  and 
not  at  a  definite  hilum. 

Of  the  lymphatics  of  the  tonsil  Httle  is  known. 

The  nerves  which  are  branches  of  the  glosso-pharyngeal  and  of 
the  spheno-palatine  ganghon  also  enter  the  organ  along  its  attached 
side. 

The  palatine  tonsils  make  their  first  appearance  during  the  third  month  of 
intra-uterine  life  as  hollow  evaginations  of  entoderm  which  grow  down  into 
the  underlying  mesenchyme,  in  the  region  of  the  second  inner  branchial 
groove.  The  earliest  of  the  tonsillar  lymphoid  cells  are  apparently  white 
blood  cells  which  have  migrated  from  the  vessels  of  the  stroma  of  the  mucosa 
and  have  infiltrated  the  surrounding  connective  tissue.  Further  development 
of  the  tonsil  is  by  proliferation  of  these  cells.  The  crypts  are  at  first  solid 
ingrowths  of  surface  epithelium.      These  later  become  hollowed  out. 

The  lingual  and  pharyngeal  tonsils  begin  their  development  during  the 
later  months  of  intra-uterine  life.  In  the  pharyngeal  tonsils,  definite  nodules 
appear  about  the  time  of  birth  or  during  the  first  or  second  year.  In  the 
lingual  tonsils  the  nodules  are  not  fully  formed  until  the  fifth  or  sixth  year. 


LYMPHATIC  ORGANS  181 


TECHNIC 


Normal  human  tonsils  are  so  rare,  owing  to  the  frequency  of  inflammation  of 
the  organ,  that  it  is  best  to  make  use  of  tonsils  from  one  of  the  lower  animals  (dog, 
cat,  or  rabbit).  Treat  as  in  technic  i,  p.  172,  care  being  taken  that  sections  pass 
longitudinally  through  one  of  the  crypts. 

The  Spleen 

The  spleen  is  a  lymphatic  organ  and  might  be  quite  properly 
classed  as  a  hasmolymph  node.  Its  peculiar  structure  appears  to 
depend  largely  upon  the  arrangement  of  its  blood-vessels. 

Except  where  attached,  the  spleen  is  covered  by  a  serous  mem- 
brane, the  peritoneum  (page  267).  Beneath  this  is  a  capsule  of  fibrous 
tissue  containing  numerous  elastic  fibres  and  some  smooth  muscle 


Fig.  105. — Section  through  Portion  of  Cat's  Spleen.^to  show  general  topography. 
XiS-  (Technic  i,  p.  187.)  a,  Capsule;  b,  septa  containing  blood-vessels;  c,  germinal 
centres;  d,  septa;  e,  lymph  nodules. 

cells.  From  the  capsule  strong  connective-tissue  septa,  similar  to 
the  capsule  in  structure,  extend  into  the  interior  of  the  organ. 
These  branch  and  unite  with  one  another  to  form  very  incomplete 
anastomosing  chambers.  The  capsule  and  septa  form,  as  in  the 
.lymph  node,  the  connective-tissue  framework  of  the  organ  (Fig.  105). 
The  chambers  incompletely  bounded  by  the  connective-tissue 
septa  are  filled  in  with  tissue  resembling  lymphatic  tissue,  composed 
of  reticular  connective  tissue,  lymphoid  cells,  and  other  varieties  of 
cells  described  on  p.  184.  This  tissue  constitutes  the  substantia 
propria  of  the  organ  and  is  everywhere  traversed  by  thin-walled 
vascular  channels,  the  tissue  and  vascular  channels  together  con- 


182  THE  ORGANS 

stituting  the  splenic  pulp  (Fig.  io6).  Compact  lymphatic  tissue 
occurs  in  the  spleen  as  spherical,  oval,  or  cyHndrical  aggregations 
of  closely  packed  lymphoid  cells.  These  are  known  as  Malpighian 
bodies  or  splenic  corpuscles  (Figs.  105  and  106)  and  are  distributed 
throughout  the  splenic  pulp.  Each  splenic  corpuscle  contains  one 
or  morejsmall  arteries.  These  usually  run  near  the  periphery  of 
the  corpuscle;  more  rarely  they  lie  at  the  centre.  Except  for  its 
relation  to  the  blood-vessels,  the  splenic  corpuscle  is  quite  similar  in 
structure  to  a  lymph  nodule.  It  consists  of  lymphoid  cells  so  closely 
packed  as  completely  to  obscure  the  underlying  reticulum.     In  a 


S5 


Fig.  106. — Section  of  Human  Spleen,  including  portion  of  Malpighian^body  with  its 
artery  and  adjacent  splenic  pulp.  X300.  (Technic  2,  p.  187.)  a,  Malpighian  body; 
b,  pulp  cords,  c,  cavernous  veins;  b  and  c  together  constituting  the  splenic  pulp. 

child's  spleen  the  centre  of  each  corpuscle  shows  a  distinct  germinal 
centre  (see  page  169).  In  the  adult  human  spleen  germ  centres  are 
rarely  seen.  The  blood-vessels  of  the  spleen  have  a  very  character- 
istic arrangement,  which  must  be  described  before  considering  further 
the  minute  structure  of  the  organ. 

The  arteries  enter  the  spleen  at  the  hilum  and  divide,  the  branches 
following  the  connective-tissue  septa.  The  arteries  are  at  first  ac- 
companied by  branches  of  the  splenic  veins.  Soon,  however,  the 
arteries  leave  the  veins  and  the  septa,  and  pursue  an  entirely  separate 
course  through  the  splenic  pulp.  Here  the  adventitia  of  the  smaller 
arteries  assumes  the  character  of  reticular  tissue  and  becomes  in- 
filtrated with  lymphoid  cells.     In  certain  animals,  as  e.g.,  the  guinea- 


LYMPHATIC  ORGANS 


183 


pig,  this  infiltration  is  continuous,  forming  long  cord-like  masses  of 
compact  lymphoid  tissue.  In  man,  the  adventitia  is  infiltrated  only 
at  points  along  the  course  of  an  artery.  This  may  take  the  form 
of  elongated  collections  of  lymphoid  cells — the  so-called  spindles — 
or  of  distinct  lymph  nodules,  the  already  mentioned  splenic  corpuscles. 
Although  usually  eccentrically  situated  with  reference  to  the  nodules, 
these  arteries  are  known  as  central  arteries.  They  give  rise  to  a  few 
capillaries  in  the  spindles,  to  a  larger  number  in  the  nodules.     Be- 


Spleen  sinus 


Sheath  artery 


Pulp  vein 


Beginning  of  in-  _ 
erlobular  vein 


Capillary  net-  ^     A 
work  of  nodule  "■    ~ 


Pulp  artery 


Trabecula 


Penicillus 


Central  artery 


Interlobular  vein 


>  Lobule 


Hiius  ■     Reticulum        Spleen  nodule  Capsule 

Fig.  107. — Scheme  of  Human  Spleen,  x,  Opening  of  arterial  capillaries  into' spleen 
sinus;  xx,  interruption  of  closed  blood  course  at  ends  of  arterial  capillaries,  at  margin  of 
nodule,  xxx.  For  sake  of  clearness,  sinus  is  placed  too  far  from  margin  of  nodule. 
(Stohr.) 

yond  the  latter  the  arteries  divide  into  thick  sheathed  terminal 
arteries — pulp  arteries — which  do  not  anastomose,  but  lie  close  to- 
gether like  the  bristles  of  a  brush  or  penicillus.  The  pulp  arteries 
break  up  into  unusually  thick  walled  arterial  capillaries  wliich  still 
retain  an  adventitia,  the  so-called  sheathed  arteries.  These  are 
of  remarkably  uniform  diameter — 6-8  cc — and  empty  into  broader 
spaces  from  10  to  40/'  in  diameter — the  spleen,  sinuses  or  ampullcB — 
which  in  turn  empty  into  the  cavernous  veins  of  the  si)lenic  pulp 
(Fig.  106). 


184 


THE  ORGANS 


A 


£ 


J) 


II 


The  Splenic  Pulp.— The  anastomosing  cavernous  veins  break 
up  the  diffuse  lymphatic  tissue  of  the  spleen  into  a  series  of  anasto- 
mosing cords  similar  to  those  found  in  the  medulla  of  the  lymph 
node.  These  are  known  as  pulp  cords  (Fig.  io6),  and  with  the  caver- 
nous veins  constitute,  as  already  mentioned,  the  splenic  pulp.  The 
pulp  cords  consist  of  a  dehcate  framework  of  reticular  connective 

tissue,  in  the  meshes  of  which  are 
found,  in  addition  to  lymphoid 
cells,  the  following  (Fig.  io8) : 

(i)  Red  blood  cells,  including 
nucleated  red  blood  cells  and 
fragments  of  red  cells  in  process 
of  disintegration. 

(2)  White  blood  cells. 

(3)  Mononuclear  cells,  the 
so-called  spleen  cells.  These 
are  rather  large,  granular,  spher- 
ical, or  irregular  cells.  From 
the  fact  that  blood  pigment  and 
red  blood  cells  in  various  stages 
of  disintegration  are  found  in 
their  cytoplasm,  these  cells  are 
beheved  to  be  concerned  in  the 


G 


J 


Fig.  108. — Isolated  Spleen  Cells.  X  700. 
(Kolliker.)  A,  Cell  containing  red  blood 
cells;  &,  blood  cell;  k,  nucleus;  B,  leucocyte 
with  polymorphous  nucleus;  C,  "spleen" 
cell  with  pigment  granules;  D,  lymphocyte; 
£,  large  cell  with  lobulated  nucleus  (megalo- 
cyte);  F,  nucleated  red  blood  cells;  G,  red 
blood  cell;  U,  multinuclear  leucocyte;  /,  cell 
containing  eosinophile  granules. 


destruction  of  red  blood  cells. 

(4)  Multinuclear  cells.  These  are  most  common  in  young  ani- 
mals. Each  cell  contains  a  single  large  lobulated  nucleus,  or  more 
frequently  several  nuclei.  These  cells  resemble  the  osteoclasts  of 
developing  bone  and  the  multinuclear  cells  of  bone-marrow. 

In  macerated  splenic  tissue  or  in  smears  from  the  spleen,  there 
are  found,  in  addition  to  the  above  varieties  of  cells,  long  spindle- 
shaped  cells  with  bulging  nuclei.  These  come  from  the  walls  of  the 
cavernous  veins. 

Two  views  have  been  held  regarding  the  vascular  channels  of  the  pulp. 
According  to  one,  these  channels  have  complete  waUs,  the  blood-vessel  system 
of  the  splenic  pulp  being  a  closed  system  as  in  other  organs.  According  to  the 
other,  the  cavernous  veins  or  spleen  sinuses  into  which  the  arterial  capillaries, 
open,  have  fenestrated  walls — open  system.  These  fenestra  are  of  sufficient  size 
to  allow  fluid  and  formed  elements  of  the  blood  to  pass  out  freely  into  the  pulp 
cords  and  elements  of  the  pulp  cords  to  pass  freely  into  the  vessels.  From  these 
open- walled  sinuses  the  veins  proper  take  origin.  The  smaller  veins,  even  those 
within  the  trabeculae,  have  only  endothelial  walls.     These  uniting,  form  veins. 


LYISIPHATIC  ORGANS 


185 


which  enter  the  septa  and  ultimately  converge  to  form  the  splenic  veins  which 
leave  the  organ  at  the  hilum. 

MoUier^  describes  the  walls  of  the  spleen  pulp  sinuses  as  having  the  following 
structure,  (i)  A  protoplasmic  endothelial  syncytium,  with  scattered  oval 
nuclei  (their  long  diameter  lying  in  the  long  diameter  of  the  vessel)  and  no 
evidence  of  cell  boundaries.  This  syncytium  is  arranged  as  a  network,  the 
meshes  of  which  are  sometimes  quite  irregular,  at  other  times  quite  regular  and 


Fig.  109. — Section  of  Monkey's  Spleen.  Two  pulp  sinuses  are  shown  and  between 
them  some  of  the  reticular  tissue  of  the  pulp.  The  sinus  in  the  upper  right  corner  is  cut 
transversely  so  that  the  longitudinal  fibres  of  its  wall  are  cut  across  and  appear  as  a  row 
of  dots.  The  prominent  dark  nuclei  belong  to  the  endothelium.  The  other  sinus  is  cut 
obliquely  and  a  branch  from  it  is  seen  partly  in  longitudinal  section.  It  shows  well  the 
disposition  of  both  longitudinal  and  circular  fibres.     (Alollicr.) 

rectangular,  with  the  long  diameter  of  the  mesh  running  in  the  long  diameter  of 
the  vessel.  This  protoplasmic  syncytium  lines  the  sinus.  (2)  Outside  the 
endothelial  syncytium  are  clo.sely-placed  longitudinal  fibres  which  lie  upon  the 
lengthwise-running  strands  of  the  protoplasmic  reticulum  (Fig.  109).  (3)  Out- 
side the  lengthwise-running  strands  transverse  fibres  or  ring  fibres  which  at 
rather  longer  intervals  encircle  the  tube  (Fig.  no).  Both  longitudinal  and  ring 
fibres  arc  connective  tissue  (reticular),  and  the  reticulum  which  they  form  is 
'Arch.  f.   mikr.  Anat.,  Hd.  Ixxvi,  1910-1 1. 


186 


THE  ORGANS 


everywhere  continuous  with  the  reticulum  of  the  pulp  cords  and  apparently- 
identical  with  it,  except  that  to  form  walls,  the  reticulum  is  flattened  out  and 
usually  has  a  more  regular  arrangement.  The  strands  of  the  fibre  reticulum  lie 
upon  the  strands  of  the  protoplasmic  reticulum  in  such  a  way  that  the  meshes 
correspond.  A  thin  structureless  fenestrated  membrane  lying  just  outside  the 
endothehal  syncytium  has  been  described.  The  sinus  walls  probably  possess  a 
certain  elasticity  or  contractility  and  undoubtedly  change  their  diameter  to 
accord  with  varying  functional  conditions.     It  follows  that  the  meshes  of  the 

reticulum  may  be  at  one  time  widely  open  (con- 
gested spleen),  at  another  partly  open,  at  still 
I        another  entirely  closed. 

0  The  main  functions  of  the  adult  spleen  in 

,  ^       health  appear  to  be  the  production  of  leuco- 

I  II        cytes  and  the  destruction  of  red  blood  cells.     It 

is  possible  that  to  a  limited  degree  the  spleen 
produces  red  blood  cells.  During  foetal  life  the 
spleen  is  actively  engaged  in  the  development  of 
both  red  and  white  cells.  Also  in  adult  life  a 
severe  secondary  anaemia  or  a  pernicious  anaemia 
may  stimulate  the  spleen  to  resume  production 
of  red  and  white  cells.  The  spleen  can  be  re- 
moved without  apparently  seriously  interfering 
with  the  body  functions.  Enlargement  of 
lymph  nodes  and  increased  blood-forming 
activity  of  bone  marrow  as  a  result,  have  been 
described. 

The  ultimate  origin  of  the  spleen  in  man  has 
not  been  definitely  determined.  The  anlage  of 
the  spleen  can  be  seen  in  embryos  of  five  weeks 
as  a  thickening  of  the  mesenchyme  in  the  left 
dorsal  mesogastrium  and  it  was  believed  that 
the  organ  developed  wholly  from  this  mesen- 
chyme. The  mesothelium  covering  the  thick- 
ened mesenchyme  also  shows  thickening,  and  demarcation  between  the  two 
layers  becomes  almost  entirely  lost.  Recent  investigations  have  made  it  seem 
probable  that  the  spleen  develops  in  part  at  least  from  these  mesothelial  cells 
which  grow  down  into  the  mesenchyme.  In  this  case  it  is  probable  that  mesen- 
chyme gives  rise  to  capsule,  trabeculae,  and  reticular  connective  tissue — the 
connective  tissue  framework  of  the  organ — while  mesothelium  is  responsible  for 
some  at  least  of  the  various  cellular  elements  of  the  splenic  pulp. 


Hi 


Fig.  iio.^ — Diagram  of  a  Sinus 
of  the  Splenic  Pulp,  showing  Re- 
lations of  Longitudinal  Fibres, 
Circular  Fibres  and  Endothelial 
Nuclei.     (Mollier.) 


Lymphatics  are  not  numerous.  In  certain  of  the  lower  animals 
large  lymph  vessels  occur  in  the  capsule  and  septa.  These  are  not 
well  developed  in  man.  Lymph  vessels  are  present  in  the  connective 
tissue  of  the  hilum.  They  probably  do  not  occur  in  the  splenic  pulp 
or  in  the  splenic  corpuscles. 


LYMPHATIC  ORGANS  187 

Nerves.- — These  are  mainly  non-meduUated,  although  a  few 
meduUated  fibres  are  present.  Among  the  latter  are  dendrites  of 
sensory  neurones  whose  cell  bodies  are  situated  in  the  spinal  gan- 
glia. They  supply  the  connective  tissue  of  the  capsule,  septa,  and 
blood-vessels.  The  non-medullated  fibres — axones  of  sympathetic 
neurones — accompany  the  arteries,  around  which  they  form  plexuses. 
From  these  plexuses  terminals  pass  to  the  muscle  cells  of  the  arteries, 
to  the  septa,  to  the  capsule,  and  possibly  also  to  the  splenic  pulp. 
The  exact  manner  in  which  both  medullated  and  non-medullated 
fibres  terminate  is  as  yet  undetermined. 

TECHNIC 

(i)  The  spleen  of  a  cat  is  more  satisfactory  for  topograpliy  tfian  the  human 
spleen,  as  it  is  smaller,  contains  more  connective  tissue  and  its  Malpighian  bodies 
are  more  evenly  distributed  and  more  circumscribed.  Fix  in  formalin-Muller's 
fluid  (technic  5,  p.  7),  and  harden  in  alcohol.  Cut  sections  through  the  entire 
spleen.  Stain  with  haematoxylin-eosin  (technic  i,  p.  20),  or  with  haematoxylin- 
picro-acid-fuchsin  (technic  3,  p.  21). 

(2)  Human  Spleen. — Small  pieces  are  treated  as  in  technic  (i). 

(3)  Human  Spleen  (Congested). — Congested  human  spleens  are  usually 
easy  to  obtain  from  autopsies.  Treat  as  in  technic  (i).  The  cavernous  veins 
being  distended  with  blood,  the  relations  of  the  veins  to  the  pulp  cords  are  more 
easily  seen  than  in  the  uncongested  spleen.  The  contrasts  are  especially  sharp 
in  sections  stained  with  haematoxylin-picro-acid-fuchsin. 

(4)  The  cells  of  the  spleen  may  be  studied  along  the  torn  edges  or  in  the  thin- 
ner parts  of  any  of  the  spleen  sections.  Or  a  smear  may  be  made  in  a  man- 
ner similar  to  that  described  in  technic  (page  no),  by  drawing  the  end  of  a 
slide  across  a  freshly  cut  spleen  surface  and  then  smearing  the  tissue  thus  ob- 
tained across  the  surface  of  a  second  slide.  Dry,  fix  in  equal  parts  alcohol  and 
ether  (one-half  hour),  stain  with  ha^matoxylin-eosin  and  mount  in  balsam.  Or 
the  cut  surface  of  the  spleen  may  be  scraped  with  a  knife,  the  scrapings  trans- 
ferred to  Zenker's  fluid,  hardened  in  alcohol,  stained  with  alum-carmine  (pages 
19  and  63)  and  mounted  in  eosin-glycerin. 

General  References  for  Further  Study 

KoUiker:  Handbuch  der  Gewebelehre  des  Menschen,  vol.  iii. 

Szymonowicz  and  MacCallum:  Histology  and  Microscopic  Anatomy. 

Warthin:  Haimolymph  Glands  (with  bibliography).  Reference  Handbook 
of  the  Medical  Sciences,  vol.  iv. 

Mall:  Lobule  of  the  Spleen.  Bui.  Johns  Hopkins  Hospital,  vol.  ix.— Archi- 
tecture and  Blood-vessels  of  the  Dog's  Spleen.     Zeit.  f.  Morph.  u.  Anth.,  Bd.  ii. 

Oppel:  Ueber  Gitterfasern  der  menschlichen  Leber  und  Milz.  Anat.  Anz.,  6 
Jahrg.,  S.  165. 


CHAPTER  III 

THE  SKELETAL  SYSTEM 

The  skeletal  system  consists  of  a  series  of  bones  and  cartilages 
which  are  united  by  special  structures  to  form  the  supporting  frame- 
work of  the  body.  Under  this  head  are  considered:  (i)  bones,  (2) 
marrow,  (3)  cartilages,  (4)  articulations. 

The  Bones 

A  bone  considered  as  an  organ  consists  of  bone  tissue  laid  down 
in  a  definite  and  regular  manner.  If  a  longitudinal  section  be  made 
through  the  head  and  shaft  of  a  long  bone,  the  head  of  the  bone  and 
also  part  of  the  shaft  are  seen  to  be  composed  of  anastomosing  bony 


Fig.   III. — Section  of  Spongy  Bone.     X7S-     (Technic  3,  p.  197.)     a,  Marrow  space;  h, 
group  of  fat  cells;  c,  blood-vessel;  d,  trabeculae  of  bone. 

trabeculae  enclosing  cavities.  This  is  known  as  cancellous  or  spongy 
hone.  The  shaft  of  the  bone  consists  of  a  large  central  cavity  sur- 
rounded by  spongy  bone,  which,  however,  passes  over  on  its  outer 
side  into  a  layer  of  bone  of  great  density  and  known  as  hard  or  compact 
hone.  Spongy  bone  forms  the  ends  and  lines  the  marrow  cavities  of 
the  long  bones,  and  occurs  also  in  the  interior  of  short  bones  and  flat 

188 


THE  SKELET.\L  SYSTEM 


189 


bones.  Compact  bone  forms  the  bulk  of  the  shafts  of  the  long  bones 
and  the  outer  layers  of  the  fiat  and  short  bones. 

In  compact  hone  the  layers  or  lamellae  of  bone  tissue  have  a  defi- 
nite arrangement  into  systems,  the  disposition  of  which  is  largely 
dependent  upon  the  shape  of  the  bone  and  upon  the  distribution  of 
its  blood-vessels. 

In  spongy  hone  (Fig.  1 1 1)  there  is  no  arrangement  of  the  bone  tissue 
into  systems.     The  trabecular  consist  wholly  of  bony  tissue  laid  down 


b^r^A>\* 


Fig.   112. — Longitudinal  Section  of  Hard  (Undccalcitied)  Bone:  Shaft  of  Human  Ulna. 
X90.     (Szymonowicz.)     Haversian  canals,  lacuna;,  and  canaliculi  in  black. 

in  lamella;.  These  trabeculae  anastomose  and  enclose  spaces  which 
contain  marrow  and  which  serve  for  the  passage  of  blood-vessels, 
lymphatics,  and  nerves. 

On  examining  a  longitudinal  section  of  compact  bone  (Fig.  112) 
there  are  seen  running  through  it  irregular  channels,  the  general 
direction  of  which  is  parallel  to  the  long  axis  of  the  bone.  These 
channels  anastomose  by  means  of  lateral  branches,  and  form  a  com- 
plete system  of  intercommunicating  tubes.  They  are  known  as 
Haversian  canals,  contain  marrow  elements,  and  serve  for  the  trans- 
mission of  blood-vessels,  lymi)hatics,  and  nerves.  They  anastomose 
not  only  with  one  another,  but  are  in  communication  with  the  sur- 


190  THE  ORGANS 


face  of  the  bone  and  with  the  central  marrow  cavity.     Between  the 
Haversian  canals  most  of  the  lamellas  run  parallel  to  the  canals. 

In  a  cross  section  through  the  shaft  of  a  long  bone  (Fig.  113),  three 
distinct  systems  of  lamellae  are  seen.  These  are  known  as  Haversian 
lamellcB,  interstitial  lamellce,  and  circumferential  lamellce. 


':v«r;/ 

/     / 


*    •  ». 


'^    If.  •^;  «..■ 


.w.'V^'  ^.-^..^'!%.^;..;.-^-  »- 


'  •■'■\''  ':   "4   >  ^    '1  1,'-  ^^^  /■  .         '  -     —    " . 


-fc-i 


.'^•:v.'^-.<n„^i^ 


Fig.  113. — Cross-section  of  Hard  (Undecalcified)  Bone  from  Human  Metatarsus. 
X90.  (Szymonowicz.)  Haversian  canals,  lacunas,  and  canaliculi  in  black,  o,  Outer 
circumferential  lamellas;  h,  inner  circumferential  lamellae;  c,  Haversian  lamellae;  d, 
interstitial  lamellae. 

(i)  Haversian  Lamella  (Fig.  114) . — These  are  arranged  in  a  con- 
centric manner  around  the  Haversian  canals.  Between  the  lamellae, 
their  long  axes  corresponding  to  the  long  axes  of  the  Haversian  canals, 
are  the  lacuna  with  their  inclosed  hone  cells  (page  loi).  The  lacunae 
of  adjacent  lamellae  are  usually  arranged  alternately.  In  a  section 
of  ordinary  thickness  the  lacunae  are  not  nearly  so  numerous  as  the 
lamellae,    and   are   seen   only   between  some  of  the  lamellae.     The 


THE  SKELET.\L  SYSTE.M 


191 


lacunae  of  a  Haversian  system  communicate  with  one  another  and 
with  their  Haversian  canal  by  means  of  the  canaliculi.  In  Haversian 
systems  the  fibres  of  the  matrix  (see  page  loi)  run  in  some  lamellae 
parallel  to  the  canal,  in  others  concentrically.  Adjacent  fibres  thus 
frequently  cross  at  right  angles. 

(2)  Interstitial  (Intermediate  or  Ground)  Lamella  (Figs. 
113  and  114). — These  are  irregular  short  lamellae,  which  occupy  the 
spaces  left  between  adjacent 
Haversian  systems. 

(3)  Circumferential  La- 
mella (Fig.  113).- — These  are 
parallel  lamellae  which  run  in 
the  long  axis  of  the  bone, 
just  beneath  the  periosteum 
and  at  the  outer  edge  of  the 
central  marrow  cavity.  Oc- 
c  a  s  i  o  n  a  1 1  y  circumferential 
lamellae  are  absent,  the  Haver- 
sian systems  abutting  directly 
upon  periosteum. 

Channels  for  the  passage 
of  blood-vessels  from  the  peri- 
osteum to  the  Haversian 
canals  pierce  the  circumfer- 
ential lamellae.  They  are 
known  as  Volkmann's  canals, 
and  are  not  surrounded  by 
concentric  ]am.ellae  as  are  the 
Haversian  lamellae,  but  are 
mere  channels  through  the 
bone.  Similar  canals  pass  from  the  inner  Haversian  canals  into  the 
marrow  cavity. 

The  Periosteum. — This  is  a  fibrous  connective-tissue  membrane 
which  covers  the  surfaces  of  bones  except  where  they  articulate. 
It  is  firmly  adherent  to  the  superficial  layers  of  the  bone  and  consists 
of  two  layers.  The  outer  layer  is  comi)osed  of  coarse  fibrillated 
fibres  and  contains  the  larger  blood-vessels.  The  inner  layer  con- 
sists of  fine  white  fibres  and  delicate  elastic  fibres  which  support  the 
smaller  blood-vessels. 

From  the  periosteum  distinct  bundles  of  white  fibres,  with  often 


Fig.  114. — Transverse  Section  of  Compact 
Bone  from  Shaft  of  Humerus.  XiSo  and 
slightly  reduced.  (Sharpey.)  (Technic  i,  p. 
196.)  Three  Haversian  canals  with  their  con- 
centric lamella;  and  lacuna;;  canaliculi  connect- 
ing lacunic  with  each  other  and  with  Haversian 
canal.  Between  the  Haversian  systems  of 
lamellae  are  seen  the  interstitial  lamella;. 


192 


THE  ORGANS 


some  elastic  fibres,  pierce  the  outer  layers  of  the  bone.  These  are 
known  as  the  perforating  fibres  of  Sharpey.  When  tendons  and  liga- 
ments are  attached  to  bone,  their  fibres  are  prolonged  through  the 
periosteum  into  the  bone  as  perforating  fibres. 


Bone  Marrow 

Bone  marrow  is  a  soft  tissue  which  occupies  the  medullary  and 
Haversian  canals  of  the  long  bones  and  fills  the  spaces  between  the 
trabeculae  of  spongy  bone.  It  consists  of  a  delicate  reticular  connec- 
tive tissue,  in  the  meshes  of  which  He  various  kinds  of  cells.  Because 
of  its  function  as  a  blood-forming  organ  it  contains  all  varieties  of 
blood  cells  as  well  as  certain  other  cells.  It  is  convenient  to  divide 
marrow  cells  primarily  into  (i)  blood  cells,  adult  and  developmental 
forms,  and  (2)  other  cells. 


Marrow  cells  . 


Blood  cells 


Other  cells 


White 


Red     i 


Adult    forrr,^  ^  Non-granular  leucocytes 

Adult   lorms  ^  Granular  leucocytes 

Developmental  forms — myelocytes 

Adult  non-nucleated 

„       ,  ,   1  J.  f  Primary  erythroblasts 

Developmental  forms  |  Secondary  erythroblnsts 


Gianf  relk  ^  Megakaryocytes 
tjiant  ceils  ^  polykaryocytes 

Fat  cells 

Plasma  cells 

Cells  of  the  reticular  tissue 


The  following  description  omits  the  adult  forms  of  blood  cells  for 
which  the  student  is  referred  to  p.  103. 

(i)  Myelocytes. — These  resemble  the  mononuclear  and  some  of  the 
transitional  forms  of  leucocytes.  The  nucleus  is  large  and  may  be 
lobulated.  It  contains  a  comparatively  small  amount  of  chromatin 
and  therefore  stains  faintly.  The  cytoplasm  is  finely  granular  and 
stains  with  neutrophile  dyes.  Myelocytes  are  not  present  in  normal 
blood,  but  occur  in  large  numbers  in  leukaemia.  It  is  from  the 
myelocytes  that  some  and  possibly  all  leucocytes,  which  are  of  bone- 
marrow  origin,  are  derived. 

(2)  Nucleated  Red  Blood  Cells. — These  are  divisible  into  primary 
erythroblasts  and  secondary  erythroblasts  or  normoblasts.  The  former 
represents  an  earUer,  the  latter  a  later  stage  in  the  evolution  of  the 
non-nucleated  adult  red  blood  cell. 

The  primary  erythroblast,  the  younger  of  the  two,  has  a  well- 
formed  nucleus  with  a  distinct  intranuclear  network.     The  proto- 


THE  SKELET.\L  SYSTEM  193 

plasm  contains  but  little  haemoglobin.  In  the  secondary  erythrohlast 
the  intranuclear  network  has  disappeared  and  the  protoplasm  has 
become  richer  in  haemoglobin.  The  secondary  erythrohlast  is  con- 
verted into  the  adult  red  blood  cell  either  by  extrusion  of  its 
nucleus,  or  by  the  disintegration  of  the  nucleus  within  the  cell  body. 

(3)  Giant  Cells. — (a)  Megakaryocytes.  These  are  from  25-30/'. 
in  diameter  and  are  distinctly  amoeboid.  They  have  an  abundant 
granular  protoplasm  which  is  usually  acidcphile,  more  rarely  baso- 
phile.  Peripherally  the  protoplasm  is  comparatively  free  from 
granules  so  that  a  clear  exoplasm  and  a  granular  endoplasm  may  be 
distinguished.  The  nucleus  varies  greatly  both  in  shape  and  size. 
It  is  usually  single;  may  be  spheroidal,  but  is  more  commonly  lobu- 
lated  with  the  lobules  arranged  in  a  circle  or  hke  the  letter  C.  There 
are  many  nucleoli  and  centrosomes.  The  latter  may  be  clumped 
or  distributed  through  the  protoplasm.  When  the  nucleus  is  circu- 
lar or  C-shaped  the  centrosomes  lie  in  the  centre.  Both  mitosis  and 
amitosis  have  been  described  in  these  cells.  The  origin  and  function 
of  the  megakaryocytes  is  unknown.  Wright  describes  them  (p.  no) 
as  giving  rise  to  the  blood  platelets,  Stohr  as  probably  associated 
with  the  formation  of  leucocytes.  They  sometimes  apparently  en- 
tirely lose  their  protoplasm,  thus  giving  rise  to  free  giant  nuclei. 

(b)  Polykaryocytes  (myeloplaxes — osteoclasts).  These  are  even 
larger  than  the  megakaryocytes,  having  sometimes  a  diameter  of 
ioo«.  They  are  flat  with  a  thickness  of  only  6-io/i  and  are  rather 
scarce  in  adult  bone.  In  developing  bone  they  are  numerous  and 
lie  near  the  bone  or  cartilage.  Their  protoplasm  is  granular  and 
frequently  contains  fat  droplets.  They  are  multinuclear  (5  to  40) 
and  contain  many  centrosomes  arranged  in  pairs,  the  number  of  pairs 
apparently  corresponding  to  the  number  of  nuclei.  The  nuclei  may 
be  clumped  near  the  centre  of  the  cell  or  may  be  arranged  in  a  ring 
or  skein  or  irregularly.  In  development  of  bone  these  cells  appa- 
rently have  to  do  with  its  absorption.  It  is  of  interest  to  note  that 
they  are  also  found  at  the  roots  of  milk  teeth  which  are  being  ab- 
sorbed, and  Billroth  describes  them  as  apparently  causing  the 
absorption  of  ivory  pegs  which  had  been  driven  into  bone. 

Fat  cells  (p.  88),  plasma  cells  (p.  85),  mast  cells  (p.  85)  and  cells 
of  the  reticular  connective  tissue  (p.  94)  arc  found  in  marrow  in 
varying  numbers. 

While  all  marrow  contains  the  elements  described,  their  propor- 
tions vary  greatly.     Dependent  upon  the  amount  of  fat  present  are 

13 


194  THE  ORGANS 

distinguished  two  main  varieties  of  marrow,  red  marrow  and  yellow 
marrow. 

Red  marrow  is  found  in  all  bones  of  embryos  and  of  young  ani- 
mals, also  in  the  vertebrae,  sternum,  ribs,  cranial  bones,  and  epiphyses 
of  long  bones  in  the  adult.  In  the  diaphyses  of  adult  long  bones 
the  marrow  is  of  the  yellow  variety.  The  difference  in  color  between 
red  marrow  and  yellow  marrow  is  due  to  the  much  greater  propor- 


14      <       if 


f^        fp- 


' 

H' 

fl 

«          "/" 

<-A               jS- 

«^^ 

,««>-.v 

V 

Fig.  115. — Section  of  Red  Bone-marrow  from  Rabbit's  Femur.  X700.  (Technic 
4,  p.  197.)  a,  Red  blood  cells;  &,  myeloplax;  c,  fat  space;  d,  nucleated  red  blood  cells; 
e,  myelocytes;  /,  reticular  connective  tissue;  g,  leucocytes. 

tion  of  fat  in  the  latter,  yellow  marrow  being  developed  from  the 
red  by  an  almost  complete  replacement  of  its  other  elements  by  fat 
cells. 

Red  marrow  is  of  especial  interest  as  a  blood-forming  tissue, 
being  in  the  healthy  adult  the  main  if  not  the  sole  source  of  red 
blood  cells,  and  one  of  the  sources  from  which  the  leucocytes  are 
derived.  (See  also  p.  109.)  At  the  same  time  it  is  quite  probable 
that  it  functionates  as  a  place  where  blood  cells  are  destroyed.  It 
is  also  active  in  the  development  of  bone. 


THE  SKELETAL  SYSTEM  195 

Yellow  marrow  (Fig.  ii6)  consists  almost  wholly  of  fat  cells, 
which  have  gradually  replaced  the  other  marrow  elements.  Under 
certain  conditions  the  yellow  marrow  of  the  bones  of  the  old  or 
greatly  emaciated  undergoes  changes  due  for  the  most  part  to  the 
absorption  of  its  fat.  Such  marrow  becomes  reddish  and  assumes 
a  somewhat  gelatinous  appearance.     It   is  known  as   '^  gelatinous 


'^•^W.     ' 


% 

'^^\^ 


^  ^.&^  s.. 


^  ^  ^~ ,d 


f  e 

Fig.  ii6. — Yellow  Marrow  from  Rabbit's  Femur.  Xs6o.  (Technic  4,  p.  197.) 
a,  nucleated  red  blood  cells;  b,  myeloplax;  c,  fat  cells;  d,  myelocytes;  e,  reticular  connec- 
tive tissue;  /,  leucocytes. 

marrow."  Under  certain  conditions,  e.g.,  fracture  of  shaft  of  long 
bone,  yellow  marrow  may  assume  the  character  of  red  marrow  and 
take  an  active  part  in  the  process  of  repair.  It  also  serves  as  a 
storage  place  for  fat. 

The  large  marrow  cavities,  such  as  those  of  the  shafts  of  the  long 
bones,  are  lined  by  a  layer  of  fibrous  connective  tissue,  the  endosteum. 

Blood-vessels. — 7'hc  blood-vessels  of  bone  pass  into  it  from  the 
periosteum.  Xear  the  centre  of  the  shaft  of  a  long  bone  a  canal 
passes  obliquely  through  the  compact  bone.     This  is  known  as  the 


196  THE  ORGANS 

nutrient  canal  and  its  external  opening  as  the  nutrient  foramen.  This 
canal  serves  for  the  passage  of  the  nutrient  vessels — usually  one  artery 
and  two  veins — to  and  from  the  medullary  cavity.  In  its  passage 
through  the  compact  bone  the  nutrient  artery  gives  off  branches  to, 
and  the  veins  receive  branches  from,  the  vessels  of  the  Haversian 
canals. 

Each  of  the  flat  and  of  the  short  bones  has  one  or  more  nutrient 
canals  for  the  transmission  of  the  nutrient  vessels. 

'  In  addition  to  the  nutrient  canals  the  surface  of  the  bone  is  every- 
where pierced  by  the  already  mentioned  (page  191)  Volkmann's 
canals,  which  serve  for  the  transmission,  of  the  smaller  vessels.  In 
compact  bone  these  vessels  give  rise  to  a  network  of  branches  which 
run  in  the  Haversian  canals.  In  spongy  bone  the  network  lies  in 
the  marrow  spaces.  Branches  from  these  vessels  pass  to  the  marrow 
cavity,  and  there  break  up  into  a  capillary  network,  which  anasto- 
moses freely  with  the  capillaries  of  the  branches  of  the  nutrient  artery. 

The  capillaries  of  marrow  empty  into  wide  veins  without  valves, 
the  walls  of  which  consist  of  a  single  layer  of  endothelium.  So  thin 
are  these  walls  that  the  veins  of  marrow  were  long  described  as  pass- 
ing over  into  open  or  incompletely  walled  spaces  in  which  the  blood 
came  into  direct  contact  with  the  marrow  elements.  These  veins 
empty  into  larger  veins,  which  are  also  valveless.  Some  of  these  con- 
verge to  form  the  vein  or  veins  which  accompany  the  nutrient  artery; 
others  communicate  with  the  veins  of  the  Haversian  canals. 

Lymphatics  with  distinct  walls  are  present  in  the  outer  layer 
of  the  periosteum.  Cleft-like  lymph  capillaries  lined  with  endothe- 
lium accompany  the  blood-vessels  in  Volkmann's  and  in  the  Haver- 
sian canals.  The  lacunce  and  canaliculi  constitute  a  complete  sys- 
tem of  lymph  channels  which  communicate  with  the  lymphatics  of 
the  periosteum,  of  Volkmann's  and  the  Haversian  canals,  and  of 
the  bone-marrow. 

Nerves, — Both  medullated  and  non-medullated  nerves  accom- 
pany the  vessels  from  the  periosteum  through  Volkmann's  canals, 
into  the  Haversian  canals  and  marrow  cavities.  Pacinian  bodies 
(page  433)  occur  in  the  periosteum.  Of  nerve  endings  in  osseous 
tissue  and  in  marrow  Httle  definite  is  known. 

TECHNIC 

(i)  Decalcified  Bone.— Fix  a  small  piece  of  the  shaft  of  one  of  the  long  bones 
—human  or  animal— in  formalin-Mxiller's  fluid  (technic  5,  p.  7)    and  decalcify 


THE  SKELET.\L  SYSTEM  197 

in  hydrochloric  or  nitric  acid  solution  (page  lo).  After  decalcifying,  wash  until 
all  traces  of  acid  are  removed,  in  normal  saline  solution  to  which  a  little  ammonia 
has  been  added.  Dehydrate,  and  embed  in  celloidin.  Transverse  and  longi- 
tudinal sections  are  made  through  the  shaft,  including  periosteum  and  edge  of 
marrow  cavity.  Stain  with  hsematoxylin-eosin  (technic  i,  p.  20)  and  mount  in 
eosin-gylcerin. 

(2)  Hard  Bone. — Transverse  and  longitudinal  sections  of  undccalcified  bone 
may  be  prepared  as  in  technic  i,  p.  102. 

(3)  Spongy  Bone. — This  may  be  studied  in  the  sections  of  decalcified  bone, 
technic  (i),  where  it  is  found  near  the  marrow  cavity.  Or  spongy  bone  from  the 
head  of  one  of  the  long  bones  or  from  the  centre  of  a  short  bone  may  be  prepared 
as  in  technic  (2). 

(4)  Red  Marrow.— Split  longitudinally  the  femur  of  a  child  or  young  ani- 
mal, and  carefully  remove  the  cylinder  of  marrow.  Fix  in  formalin-Miiller's 
fluid  and  harden  in  graded  alcohols.  Cut  sections  as  thin  as  possible,  stain 
with  haematoxylin-eosin,  and  mount  in  balsam. 

(5)  ]\Iarrow:  fresh  specimen. — By  means  of  forceps  or  a  vice,  squeeze  out  a 
drop  of  marrow  from  a  young  bone,  place  on  the  centre  of  a  mounting  slide, 
cover  and  examine  it  immediately. 

(6)  Place  a  similar  drop  of  marrow  on  a  cover-glass  and  cover  with  a  second 
cover-glass.  Press  the  covers  gently  together,  slide  apart  and  fix  the  specimen 
by  immersion  for  five  minutes  in  saturated  aqueous  solution  of  mercuric  chlorid. 
Wash  thoroughly,  stain  with  haematoxylin-eosin,  and  mount  in  balsam. 

Development  of  Bone 

The  forms  of  bones  are  first  laid  down  either  in  cartilage  or  in  embryonic 
connective  tissue.  The  bones  of  the  trunk,  extremities,  and  parts  of  the  bones 
of  the  base  of  the  skull  develop  in  a  matrix  of  cartilage.  This  is  known  as  in- 
tracarlilagi>ious  or  endochondral  ossification.  The  flat  bones,  those  of  the  vault 
of  the  cranium  and  most  of  the  bones  of  the  face,  are  developed  in  a  matrix  of 
fibrillar  connective  tissue — intraniemhranous  ossification.  A  form  of  bone 
development,  similar  in  character  to  intramembranous,  occurs  in  connection 
with  both  intramembranous  ossification  and  intracartilaginous  ossification. 
This  consists  in  the  formation  of  bone  just  beneath  the  perichondrium— 5«&- 
perichondrial  ossification— ot,  as  with  the  development  of  bone  perichondrium 
becomes  periosteum — subperiosteal   ossification. 

There  are  thus  three  forms  of  bone  development  to  be  considered:  (i) 
Intramembranous,  (2)  intracartilaginous,  and  (3)  subperiosteal. 

I.  Intramembranous  Development  (Fig.  117).— In  intramembranous  ossifi- 
cation the  matrix  in  whith  the  bone  is  developed  is  connective  tissue.  The 
process  of  bone  formation  begins  at  one  or  more  points  in  this  matrix.  These 
are  known  as  ossilication  centres.  Here  some  of  the  bundles  of  white  fibres  be- 
come calcified,  i.e.,  become  impregnated  with  lime  salts.  There  is  thus  first 
established  a  centre  or  centres  of  calcification.  Between  the  bundles  of  calcified 
fibres  the  connective  tissue  is  rich  in  cells  and  vascular,  and  from  its  future  r61e 
in  bone  formation  is  known  as  osleogenclic  tissue  (Fig.  117).     .Mong  the  surfaces 


198 


THE  ORGANS 


of  the  calcified  fibres  certain  of  the  osteogenetic  cells  arrange  themselves  in  a 
single  layer  (Figs.  117  and  118).  These  are  now  known  as  osteoblasts  or  "hone 
formers."  Under  the  influence  of  these  osteoblasts  a  thin  plate  of  bone  is  formed 
between  themselves  and  the  calcified  fibres.  This  plate  of  bone  at  first  contains 
no  cells,  but  as  the  lameUa  of  bone  grows  in  thickness,  the  layer  of  osteoblasts 
becomes  completely  enclosed  by  bone.  The  osteoblasts  are  thus  transformed 
into  hone  cells  (Fig.  118),  the  spaces  in  which  they  lie  becoming  honelacunoe.  The 
bone  cell  is  thus  seen  to  be  derived  from  the  embryonic  connective-tissue  cell, 
the  osteoblast  being  an  intermediate  stage  in  its  development.     In  this  way 


~:^h 


Fig.  1 1 7. — Intramembranous  Bone  Development.  Vertical  section  through  parietal 
bone  of  human  foetus.  X160.  (Technic  i,  p.  203.)  a,  Osteoblasts;  b,  bone  trabeculse; 
c,  osteoclasts  lying  in  Howship's  lacunae;  d,  internal  periosteum;  e,  bone  cells;/,  calcified 
fibres;  g,  osteogenetic  tissue;  h,  external  periosteum  (pericranium.) 


irregular  anastomosing  trabeculae  of  bone  are  formed  enclosing  spaces  (Fig. 
117).  The  bony  trabeculas  at  first  contain  remains  of  calcified  connective- 
tissue  fibres,  while  the  spaces,  which  are  known  as  primary  marrow  spaces,  con- 
tain blood-vessels,  osteogenetic  tissue,  and  developing  marrow.  The  osteo- 
blasts ultimately  disappear  and  the  spaces  are  then  occupied  by  blood-vessels 
and  marrow.  The  connective-tissue  membrane  has  now  been  transformed  into 
cancellous  or  spongy  bone  (Fig.  iii). 

The  bone  thus  formed  is  covered  on  its  outer  surface  by  a  layer  of  con- 
nective tissue,  a  part  of  the  membrane  in  which  the  bone  was  formed,  but 
which  from  its  position  is  now  known  as  the  periosteum,  or,  in  the  case  of  the 
cranial  bones,  as  the  peri-  or  epicranium  (Fig.  117). 


THE  SKELETAL  SYSTEM  199 

In  this  form  of  bone  development,  occurring  as  it  does  in  the  bones  of  the 
skull,  provision  must  be  made  for  increase  in  the  size  of  the  cranial  cavity  to  ac- 
commodate the  growing  brain.  This  is  accomplished  in  the  following  manner: 
Along  the  surface  of  the  bone,  directed  toward  the  brain,  large  multinuclear 
cells — osteoclasts  or  "bone  breakers^' — -make  their  appearance  (Fig.  ii8).  The 
origin  of  these  cells  is  not  clear.  Similar  cells  are  conspicuous  elements  of  adult, 
marrow.  They  have  been  variously  described  as  derived  from  leucocytes 
from  osteoblasts,  or  directly  from  the  connective-tissue  cells.  A  recent  theory 
holds  that  they  are  derived  by  a  process  of  budding  from  the  endothelial  ceUs, 
which  form  the  walls  of  the  capillaries.  These  osteoclasts  apparently  possess 
the  power  of  breaking  down  bone.  They  are  found  mainly  along  its  inner  sur- 
face, and  can  be  seen  lying  in  little  depressions — ■Howship's  lacunce  (Fig.  ii8) — 


1 

e  d  c 

Fig.  ii8. — Intramembranous  Bone  Development.  Vertical  section  through  parietal 
bone  of  human  foetus.  X350.  (Technic  i,  p.  203.)  a,  Osteoblasts;  b,  calcified 
fibres;  c,  osteogenetic  tissue;  d,  osteoclast  lying  in  Howship's  lacuna;  c,  bone  lacunae; 
/,  bone. 

which  they  have  hollowed  out  in  the  bone.  Between  the  outer  surface  of  the 
bone  and  the  pericranium  is  a  layer  of  osteogenetic  tissue,  the  innermost  cells  of 
which  are  arranged  as  osteoblasts  along  the  outermost  osseous  lamellae.  Here 
they  are  constantly  adding  new  bone  beneath  the  pericranium.  This  new  bone 
is  laid  down,  not  in  flat,  evenly  disposed  layers,  but  in  the  form  of  anastomos- 
ing trabecular  enclosing  marrow  spaces. 

It  is  thus  seen  that  subperiosteal  bone,  like  intramembranous,  is  at  first  of 
the  spongy  variety,  and  that  with  the  development  of  the  cranium  the  original 
intramembranous  bone  is  entirely  absorbed,  together  with  much  of  the  sub- 
periosteal. 

2.  Intracartilaginous  Development. — In  this  form  of  ossification  an  embry- 
onal type  of  hyaUne  cartilage  precedes  the  formation  of  bone,  the  cartilage  corre- 
sponding more  or  less  closely  in  shape  to  the  future  bone  (Fig.  119).  Covering 
the  surface  of  the  cartilage  is  a  membrane  of  fibrillar  connective  tissue,  the  peri- 
chondriiwt  or  primary  periosteum. 

In  most  of  the  long  bones  the  earliest  changes  take  place  within  the  cartilage 
at  about  the  centre  of  the  shaft  (Fig.  119).     Here  the  cartilage  cells  increase  in 


200 


THE  ORGANS 


/ 


size  and  in  number  in  such  a  way  that  several  enlarged  cartilage  cells  come  to 
lie  in  a  single  enlarged  cell  space,  and  the  cartilage  assumes  the  character  of 
hyaline  cartilage.  The  cell  groups  next  arrange  themselves  in  rows  or  columns, 
which  at  first  extend  outward  in  a  radial  manner  from  a  common  centre,  but 
later  lie  in  the  long  axis  of  the  bone.  During  these  changes  in  the  cells  there  is 
_  --  an  increase  in  the  intercellular  matrix  and  a  de- 

posit there  of  calcium  salts.  In  this  way  the  car- 
tilage becomes  calcified,  the  area  involved  being 
known  as  the  calcification  centre.  Further  growth 
of  cartilage  at  the  calcification  centre  now  ceases 
and,  as  growth  of  cartilage  at  the  ends  of  the  bone 
continues,  the  central  portion  of  the  shaft  appears 
constricted.  The  changes  up  to  this  point  seem  to 
be  preparatory  to  actual  bone  formation. 

Ossification  proper  begins  by  blood-vessels  from 
the  periosteum^  pushing  their  way  into  the  calci- 
fied cartilage  at  the  calcification  centre,  carrying 
with  them  some  of  the  osteogenetic  tissue  from 
beneath  the  periosteum.  These  blood-vessels  with 
their  accompanying  osteogenetic  tissue  are  known 
as  periosteal  buds  (Fig.  120).  Osteoblasts  now 
develop  from  the  osteogenetic  tissue  and  appear 
to  dissolve  the  calcified  cartilage  from  in  front  of 
the  advancing  vessels.  In  this  way  the  septa 
between  the  cartilage  cell  spaces  are  broken  down, 
the  cartilage  cells  disappear,  and  a  central  cavity 
is  formed — the  primary  marrow  cavity.  From  tjie 
region  of  the  primary  marrow  cavity  blood-vessels 
and  osteogenetic  tissue  push  in  both  directions 
toward  the  ends  of  the  cartilage  which  is  to  be 
replaced  by  bone.  These  break  down  the  trans- 
verse septa  between  the  cell  spaces,  whUe  many  of 
the  longitudinal  septa  at  first  remain  to  form  the 
walls  of  long  anastomosing  channels,  the  primary 
marrow  spaces  (Fig.  121).  As  in  intramembranous 
bone,  these  contain  blood-vessels,  embryonal  mar- 
row, and  osteoblasts,  all  of  which  are  derived 
from  the  osteogenetic  tissue  brought  in  from  the 
periosteum  by  the  periosteal  buds.  The  osteo- 
blasts next  arrange  themselves  in  a  single  layer 
along  the  remains  of  the  calcified  cartilage,  where 
they  proceed  to  deposit  a  thin  layer  of  bone  between  themselves  and  the  cartilage 
(Fig.  122).  As  this  increases  in  thickness  some  of  the  osteoblasts  are  enclosed 
within  the  newly  formed  bone  to  become  hone  cells,  while  the  remains  of  the 
cartilage  diminishes  in  amount  and  finally  disappears.     The  calcification  centre 

^ The  term  "periosteum"  is  admissible  from  the  fact  that  the  first  bone  actually 
formed  is  beneath  the  perichondrium,  which  thus  becomes  converted  into    periosteum 


Fig.  119. — Intracartilagin- 
ous  Bone  Development. 
Longitudinal  section  of  one  of 
the  bones  of  embryo  sheep's 
foot,  showing  ossification  cen- 
tre. X20.  (Technic  2,  p. 
203.)  a,  Periosteum;  h,  blood- 
vessels; c,  subperiosteal  bone; 
d,  intracartilaginous  bone;  e, 
osteogenetic  tissue;  /,  carti- 
lage; g,  ossification  centre;  h, 
calcification  zone. 


THE  SKELET.\L  SYSTE:\I 


201 


has  now  become  the  ossification  centre,  and  its  anastomosing  osseous  trabecule, 
with  their  enclosed  spaces  containing  osteogenetic  tissue  and  marrow,  constitute 
primary  spongy  hone. 

At  either  end  of  the  ossification  centre  the  cartilage  presents  a  special  struc- 
ture. Nearest  the  centre  the  cell  spaces  are  enlarged,  flattened,  arranged  in 
rows  and  contain  shrunken  cells.  Some  of  the  walls  break  down  and  irregular 
spaces  are  formed.  The  ground  substance  is  calcified.  Passing  away  from  the 
ossification  centre,,  the  cell  spaces  become  less  flattened,  still  arranged  in  rows, 


V 


k  ■V-:^ 


m 


d-. 


"-"M^^^^ 


Fig.  1 20. 


Fig.  121. 


Fig.  120. — Intracartilaginous  Bone  Development.  X3S0.  Showing  osteogenetic 
tissue  pushing  its  way  into  the  cartilage  (periosteal  bud)  at  the  ossification  centre. 
a,  Periosteum;  /;,  cartilage  cell  spaces;  c,  periosteal  bud;  d,  blood-vessel;  e,  cartilage 
cells;/,  cartilage  matrix. 

Fig.  121. — Intracartilaginous  Bone  Development.  Same  specimen  asFig.  iJ9(X3So), 
showing  osteogenetic  tissue  pushing  its  way  into  the  cartilage  and  breaking  it  uj)  into 
trabeculae;  also  formation  of  primary  marrow  si)aces  and  disintegration  of  cartilage 
cells,  a,  Disintegrating  cartilage  cells;  6,  cartilage  trabccula;  c,  osteogenetic  tissue  in 
primary  marrow  space;  d,  blood-vessels;  e,  cell  spaces;/,  cartilage  cells. 


the  contained  cells  larger,  and  there  is  a  lesser  degree  of  calcification.  This 
area  passes  over  into  an  area  of  hyaline  cartilage  which  blends  without  distinct 
demarcation  with  the  ordinary  embryonal  cartilage  of  the  rest  of  the  shaft. 
The  area  of  calcified  cartilage  at  cither  end  of  the  os.sification  centre  is  known 
as  the  calcification  zone  and  everywhere  precedes  the  formation  of  true  bone 
(Fig.  no). 

3.  Subperiosteal  or  subperichondrial  development  (Fig.  119)  has  already 
been  largely  described  in  connection  with  intramembranous  ossification,  and 


202 


THE  ORGANS 


differs  in  no  important  respect  from  the  latter.  It  always  accompanies  one  of 
the  other  forms  of  ossification.  Bone  appears  beneath  the  perichondrium  some- 
what earlier  than  within  the  underlying  cartilage.  Beneath  the  perichondrium 
is  a  layer  of  richly  cellular  osteogenetic  tissue.  The  cells  of  this  tissue  nearest 
the  cartilage  become  osteoblasts  and  arrange  themselves  in  a  single  layer  along 
its  surface.  Under  their  influence  bone  is  laid  down  on  the  surface  of  the  carti- 
lage in  the  same  manner  as  in  intramembranous  ossification. 

Intracartilaginous  and  subperiosteal  bone  can  be  easily  differentiated  by  the 
presence  of  cartilaginous  remains  in  the  former  and  their  absence  in  the  latter. 

All  bone  is  at  first  of  the  spongy  variety.  When  this  is  to  be  converted  into 
compact  bone,  there  is  first  absorption  of  bone  by  osteoclasts,  with  increase  in 
size  of  the  marrow  spaces  and  reduction  of  their  walls  to  thin  plates.  These 
spaces  are  now  known  as  Haversian  spaces. 


i  h 

Fig.  122. — Intracartilaginous  Bone  Development.  Same  specimen  as  Fig.  119. 
(Xssc),  showing  bone  being  deposited  around  one  of  the  trabeculse  of  cartilage,  a, 
Blood-vessel;  h,  bone;  c,  cartilage  remains;  d,  bone  cell;  e,  cartilage  cell  space;/,  osteo- 
blasts; g,  osteogenetic  tissue;  h,  lamella  of  bone;  i,  connective-tissue  cells;  j,  cartilage  cell. 

Within  these  new  bone  is  deposited.  This  is  done  by  osteoblasts  which  lay 
down  layer  within  layer  of  bone  until  the  Haversian  space  is  reduced  to  a  mere 
channel,  the  Haversian  canal.  In  this  way  are  formed  the  Haversian  canals 
and  the  Haversian  systems  of  lamellcB.  Some  of  the  interstitial  lamellae  are  the 
remains  of  the  spongy  bone  which  was  not  quite  removed  in  the  enlargement  of 
the  primary  marrow  spaces  to  form  the  Haversian  spaces;  other  interstitial 
lamellae  appear  to  be  early  formed  Haversian  lamellae  which  have  been  more  or 
less  replaced  by  Haversian  lamellae  formed  later. 

While  these  varieties  of  ossification  have  been  described,  we  would  emphasize 
the  essential  unity  of  the  process.  The  likeness  between  intramembranous  and 
subperiosteal  ossification  has  been  already  noted.  The  differences  observed  in 
intracartilaginous  ossification  are  more  apparent  than  real.  In  intracartilagi- 
nous ossification  the  bone  is  developed  in  cartilage  but  not  from  cartilage.  As 
in  intramembranous  and  in  subperiosteal  ossification,  intracartilaginous  bone 
is  developed /roTO  osteogenetic  tissue.  This  osteogenetic  tissue  is  a  differentiation 
of  embryonal  connective  tissue,  in  this  case  carried  into  the  cartilage  from  the 


THE  SKELET.\L  SYSTEM  203 

periosteum  in  the  periosteal  buds.  In  intramembranous  ossification  the  bone 
is  developed  untJiin  and  directly  from  the  embryonal  connective  tissue  of  which 
the  membrane  is  composed.  In  intracartilaginous  ossification  there  is  the  same 
embryonal  connective-tissue  membrane,  but  within  this  membrane  the  form  of 
the  bone  is  first  laid  down  in  embryonal  cartilage.  Surrounding  the  cartilage 
there  remains  the  embryonal  connective  tissue  of  the  membrane,  now  perichon- 
drium. It  is  from  tissue  which  grows  into  the  cartilage  from  this  membrane — ■ 
embryonal  connective  tissue — that  the  bone,  although  developed  in  cartilage,  is 
formed. 

Marrow  develops  from  the  mesenchymal  tissue  which  enters  the  cartilage 
anlage  in  the  periosteal  buds,  at  the  beginning  of  ossification. 

Growth  of  Bone 

The  growth  of  intramembranous  bone  by  the  formation  of  successive  layers 
beneath  the  periosteum  has  been  already  described  (page  198). 

Intracartilaginous  bones  grow  both  in  diameter  and  in  length. 

Growth  in  diameter  is  accomplished  by  the  constant  deposition  of  new  layers 
of  bone  beneath  the  periosteum.  During  this  process,  absorption  of  bone  from 
\A'ithin  by  means  of  osteoclasts  leads  to  the  formation  of  the  marrow  cavity.  The 
hard  bone  of  the  shaft  of  a  long  bone  is  entirely  of  subperiosteal  origin,  the  intra- 
cartilaginous bone  being  completely  absorbed. 

Growth  in  length  takes  place  in  the  following  manner:  Some  time  after  the 
beginning  of  ossification  in  the  shaft  or  diaphysis,  independent  ossification 
centres  appear  in  the  ends  of  the  bone  (epiphyses).  So  long  as  bone  is  growing, 
the  epiphyses  and  diaphysis  remain  distinct.  Between  them  lies  a  zone  of  grow- 
ing cartilage,  the  epiphyseal  or  intermediate  cartilage.  Increase  in  length  of  the 
bone  takes  place  by  a  constant  extension  of  ossification  into  this  cartilage  from 
the  ossification  centres  of  the  epiphyses  and  diaphysis.  After  the  bone  ceases  to 
grow  in  length,  the  epiphyses  and  diaphysis  become  firmly  united. 

TECHNIC 

(i)  Developing  Bone — Intramembranous. — Small  pieces  are  removed  from 
near  the  edge  of  the  parietal  bone  of  a  new-born  child  or  animal.  These  pieces 
should  include  the  entire  thickness  of  bone  with  the  attached  scalp  and  dura 
mater.  Treat  as  in  technic  i,  p.  ig6,  except  that  the  sections  which  arc  cut  per- 
pendicular to  the  surface  of  the  bone  should  be  stained  with  ha^matoxylin-picro- 
acid-fuchsin  (technic  3,  p.  21)  and  mounted  in  balsam. 

(2)  Developing  Bone — Intracartilaginous  and  Subperiosteal. — Remove  the 
forearms  and  legs  of  a  human  or  animal  embryo  by  cutting  through  the  elbow, 
and  knee-joints.  (Fcetal  pigs  from  five  to  six  inches  long  are  very  satisfactory.) 
Treat  as  in  technic  (i).  Block  so  that  the  two  long  bones  will  lie  in  such  a  plane 
that  both  will  be  cut  at  the  same  time.  Cut  thin  longitudinal  sections  through 
the  ossification  centres,  stain  with  hiematoxylin-picro-arid-fuchsin,  and  mount 
in  balsam.  Cut  away  the  ends  of  one  or  two  of  the  embedded  bones,  leaving 
only  the  ossification  centres.  Block  so  as  to  cut  transverse  sections  through  the 
ossification  centre.     Stain  and  mount  as  the  preceding. 


204  THE  ORGANS 

In  the  picro-acid-fuchsin  stained  sections  of  developing  bone  the  cartilage  is 
stained  blue;  cells,  including  red  blood  cells,  yellow;  connective  tissue  from  pale 
pink  to  red,  according  to  density;  bone  a  deep  red. 

The  Cartilages 

The  costal  cartilages  are  hyaline.  They  are  covered  by  a  closely 
adherent  connective-tissue  membrane,  the  perichondrium.  Where 
cartilage  joins  bone  there  is  a  firm  union  between  the  two  tissues 
and  the  perichondrium  becomes  continuous  with  the  periosteum. 

The  articular  cartilages  are  described  below  under  articulations. 

The  other  skeletal  cartilages,  such  as  those  of  the  larynx,  trachea, 
bronchi,  and  of  the  organs  of  special  sense,  are  more  conveniently 
considered  with  the  organs  in  which  they  occur. 

Articulations 

Joints  are  immovable  (synarthrosis)  or  movable  (diarthrosis) .  In 
synarthrosis  union  may  be  cartilaginous  (synchondrosis),  or  by  means 
of  fibrous  connective  tissue  (syndesmosis) . 

Synchondrosis. — The  cartilage  is  usually  of  the  fibrous  form 
except  near  the  edge  of  the  bone,  where  it  is  hyaline.  The  interver- 
tebral discs  consist  of  a  ring  of  fibro-cartilage  surrounding  a  central 
gelatinous  substance,  the  nucleus  pulposus,  the  latter  representing 
the  remains  of  the  notochord. 

Syndesmosis. — Union  is  by  means  of  Hgaments.  These  may 
consist  wholly  of  fibrous  tissue,  the  fibres  and  cells  being  arranged 
much  as  in  tendon,  or  mainly  of  coarse  elastic  fibres  separated  by 
loose  fibrous  tissue.  In  such  syndesmoses  as  the  sutures  of  the  cranial 
bones,  the  union  is  by  means  of  short  fibrous  ligaments  between  the 
adjacent  serrated  edges. 

Diarthrosis. — In  diarthrosis  must  be  considered  (a)  the  artic- 
ular cartilages,  (b)  the  glenoid  ligaments  and  interarticular  cartilages, 
(c)  the  joint  capsule. 

(a)  Articular  cartilages  cover  the  ends  of  the  bones.  They  are 
of  the  hyahne  variety,^  being  the  remains  of  the  original  cartilag- 
inous matrix  in  which  the  bones  are  formed.  Next  to  the  bone  is  a 
narrow  strip  of  cartilage  in  which  the  matrix  is  calcified.     This  is 

1  In  the  acromio-clavicular,  sterno-clavicular,  costo- vertebral,  and  maxillary  articu- 
lations the  cartilage  is  of  the  fibrous  form.  The  same  is  true  of  the  cartilage  covering 
the  head  of  the  ulna,  while  the  surface  of  the  radius,  which  enters  into  the  wrist-joint, 
is  covered  not  by  cartilage,  but  by  dense  fibrous  tissue. 


THE  SKELET.\L  SYSTEM  205 

separated  from  the  remaining  uncalcified  portion  of  the  cartilage  by 
a  narrow  so-called  "striated"  zone.  The  most  superficial  of  the 
cartilage  cells  are  arranged  in  rows  parallel  to  the  surface;  in  the  mid- 
region  the  grouping  of  cells  is  largely  in  twos  and  fours  as  in  ordinary 
hyahne  cartilage  (page  98) ;  while  in  the  deepest  zone  of  the  uncal- 
cified cartilage  the  cells  are  arranged  in  rows  perpendicular  to  the 
surface. 

(b)  The  glenoid  ligaments  and  interarticular  cartilages  conform 
more  to  the  structure  of  dense  fibrous  tissue  than  to  that  of  cartilage. 

(c)  The  joint  capsule  consists  of  two  layers,  an  outer  layer  of 
dense  fibrous  tissue  intimately  blended  with  the  ligamentous  struc- 
tures of  the  joint  and  known  as  the  stratum  fihrosum,  and  an  inner 
layer,  the  stratum  synoviale  or  synovial  membrane,  which  forms  the 
lining  of  the  joint  cavity.  The  outer  part  of  the  stratum  synoviale 
consists  of  areolar  tissue  with  its  loosely  arranged  white  and  elastic 
fibres  interlacing  in  all  directions  and  scattered  connective-tissue  cells 
and  fat  cells.  Nearer  the  free  surface  of  the  membrane  the  fibres 
run  parallel  to  the  surface  and  the  cellular  elements  are  more  abun- 
dant. The  cells  are  scattered  among  the  fibres  and  are  stellate  branch- 
ing cells  like  those  usually  found  in  fibrous  connective  tissue.  On  the 
free  surface,  however,  the  cells  He  close  together,  in  places  forming  a 
single  surface  layer,  in  other  places  being  disposed  in  three  or  four  lay- 
ers. Formerly  described  as  endothelium,  they  are  now  generally 
considered  connective- tissue  cells  or  "mesenchymal  epithelium." 

From  the  free  surfaces  of  synovial  membranes,  processes  {syno- 
vial villi — Haversian  frifiges)  Y^ioitct  into  the  joint  cavity.  Some  of 
these  are  non-vascular  and  consist  mainly  of  stellate  cells  similar  to 
those  of  the  synovial  membrane.  Others  have  a  distinct  core  of 
fibrous  tissue  containing  blood-vessels  and  covered  with  stellate  con- 
nective-tissue cells.  From  the  primary  villi  small  secondary  non- 
vascular villi  are  frequently  given  off. 

TECHNIC 

(i)  Joint  Capsule  and  Articular  Cartilage. — Remove  one  of  the  small  joints 
— human  or  animal — cutting  the  bones  through  about  one-half  inch  back  from 
the  joint.  Treat  as  in  technic  i,  p.  196,  making  longitudinal  sections  through  the 
entire  joint. 

(2)  Synovial  Villi. — Remove  a  piece  of  the  capsular  ligament  from  near  the 
border  of  the  patella  and  cut  out  a  bit  of  the  velvety  tissue  which  lines  its  inner 
surface.     Examine  fresh  in  a  drop  of  normal  salt  solution.     Fix  a  second  piece 


206  THE  ORGANS 

of  the  ligament  in  formalin7Muller's  fluid  (technic  5,  p.  7),  make  sections  per- 
pendicular to  the  surface,  stain  with  haematoxylin-eosin  (technic  i,  p.  20),  and 
mount  in  balsam. 

General  References  for  Further  Study 

Braunca:  Precis  d'Histologie. 
KoUiker:  Handbuch  der  Gewebelehre,  vol.  i. 
Stohr:  Text-book  of  Histology. 

Schafer:   Histology  and  Microscopical  Anatomy,  in  Quain's  Elements  of 
Anatomy. 


CHAPTER  IV. 
THE  MUSCULAR  SYSTEM^ 

The  voluntary  muscular  system  consists  of  a  number  of  organs — 
the  muscles — and  of  certain  accessory  structures — the  tendons,  tendon 
sheaths,  and  hursa. 

A  VOLUNTARY  MUSCLE  consists  of  Striated  muscle  fibres  arranged 
in  bundles  or  fascicles  and  supported  by  connective  tissue. 

The  entire  muscle  is  enclosed  by  a  rather  firm  connective-tissue 
sheath  or  capsule — the  epimysium  (Fig.  123).     This  sends  trabeculae 


Fig.  123.  —From  a  Transverse  Section  of  a  Small  Human  Muscle,  showing  relations 
of  muscle  fibres  to  connective  tissue,  a,  Epimysium;  b,  perimysium;  c,  muscle  fibres; 
d,  arteries;  e,  endomysium. 


of  more  loosely  arranged  connective  tissue  into  the  substance  of  the 
muscle.  These  divide  the  muscle  fibres  into  bundles  or  fascicles. 
Around  each  fascicle  the  connective  tissue  forms  a  more  or  less  definite 

*  Definite  arrangements  of  smooth  muscle,  such  as  arc  found  in  the  stomach  and 
intestines,  also  the  muscle  of  the  heart,  are  properly  a  part  of  the  muscular  system. 
They  are,  however,  best  considered  under  tissues  and  in  connection  with  the  organs 
in  which  they  occur. 

207 


208 


THE  ORGANS 


'    ( 
/, 

(         1       1 

1 1 

i  I 


\i 


envelope,  the  perifascicular  sheath  or  perimysium.  From  the  latter 
delicate  strands  of  connective  tissue  pass  into  the  fascicles  between 
the  individual  muscle  fibres.  This  constitutes  the  intrafascicular 
connective  tissue  or  endomysium,  which  everywhere  completely 
separates  the  fibres  from  one  another  so  that  the  sarcolemma  of  one 
fibre  never  comes  in  contact  with  the  sarcolemma  of  any  other  fibre. 
It  should  be  noted  that  these  terms  indicate  merely  location;  epi-, 

peri-,  and  endo-mysium  all 
being  connective  tissue  grad- 
ing from  coarse  to  fine,  as  it 
passes  from  without  inward. 
The  structure  of  the  muscle 
as  an  organ  is  thus  seen  to 
conform  to  the  structure  of 
other  organs,  in  that  it  is  sur- 
rounded by  a  connective- 
tissue  capsule,  wliich  sends 
septa  into  the  organ,  dividing 
it  into  a  number  of  compart- 
ments and  serving  for  the 
support  of  the  essential  tissue 
of  the  organ,  the  muscle  fibres 
or  parenchyma. 

The  structure  of  tendon 
has  been  described  (see  page 
91). 

Tendon  sheaths  and  burses 
are  similar  in  structure,  con- 
sisting of  mixed  white  and  elastic  fibres.  Their  free  surfaces  are 
usually  lined  by  flattened  connective  tissue-cells. 

At  the  junction  of  muscle  and  tendon,  the  muscle  fibre  with 
its  sarcolemma  ends  in  a  rounded  or  blunt  extremity  (Fig.  63,  p.  119). 
Here  the  fibrils  of  the  tendon  fibres  are  in  part  cemented  to  the  sar- 
colemma, and  in  part  are  continuous  with  the  fibres  of  the  endo-  and 
peri-mysium.  This  has  been  for  a  long  time  the  accepted  idea 
of  the  transition  from  muscle  to  tendon,  and  is  perhaps  more  nearly 
correct  where  the  insertion  is  oblique.  It  has  been  more  recently 
proved,  however,  that  for  some  muscles  at  least,  and  especially  where 
muscle  and  tendon  join  end  to  end  a  much  more  intimate  union  of 
elements  occurs.     This  is  shown  in  Figs.  125  and  126  from  Stohr. 


lUj 


I 


Fig.  124. — From  a  Longitudinal  Section 
through  Junction  of  Muscle  and  Tendon. 
XiSo.  (Bohm  and  Davidoff.)  a,  Tendon;  b, 
line  of  union  showing  increase  in  number  of 
muscle  nuclei;  c,  muscle. 


THE  MUSCULAR  SYSTEM 


209 


In  Fig.  125  the  individual  muscle  fibrillae  are  seen  passing  over  into 
tendon  fibrillae  with  no  line  of  demarcation.  In  Fig.  126  a  similar 
continuity  is  shown  except  that  groups  of  muscle  fibrillse  are  seen  to 
be  continuous  with  groups  of  tendon  fibrillae.  Both  sarcoplasm, 
which  appears  somewhat  augmented  at  this  point,  and  sarcolemmae, 
extend  between  the  tendon  bundles  beyond  the  line  of  cross  muscle 
striations.  Along  the  fine  of  union  of  muscle  and  tendon  the  muscle 
nuclei  are  more  numerous  than  elsewhere  (Fig.  124,  b),  and  it  has 
been  suggested  that  there  is  here  a  zone  of  indifferent  or  formative 


Jjj  ■;:,,-,    mV' 


ill  ta  teiMi  Sa 


,-    Krause  line 
,    Dark  band 


Transition  zone  .v- 


Tendon  fibrils 


Nucleus 


Fig.  125. — Longitudinal  Section  through  Muscle- tendon  Junction:  Human  Intercostal. 
X750.     Only  part  of  a  fibre  is  shown,  without  sarcolemma.     (Stohr.) 


tissue  which  is  capable  of  developing  on  the  one  hand  into  muscle, 
on  the  other  into  the  connective  tissue  of  tendon. 

Growth  of  muscle  takes  place  mainly  at  the  ends  of  the  fibres 
where  the  nuclei  are  most  numerous.  In  addition  to  the  growth 
incident  to  increase  in  size  of  the  individual  or  of  the  particular 
muscle,  there  is  a  constant  wearing  out  of  muscle  fibres  and  their 
replacement  by  new  fibres.  This  is  accomplished  as  follows:  The 
muscle  fibre  first  breaks  up  into  a  number  of  segments  (sarcostylcs), 
some  of  which  contain  nuclei  while  others  are  non-nucleated.  The 
sarcostylcs  next  divide  into  smaller  fragments,  and  finally  completely 
disintegrate.  This  is  followed  by  a  process  of  absorption  and  com- 
plete disappearance  of  the  fibre.     From  the  free  sarcoplasm  new 

14 


210  THE  ORGANS 

muscle  fibres  are  formed.  In  the  early  stages  of  their  development 
these  are  known  as  myoblasts.  The  latter  develop  into  muscle 
fibres  in  the  same  manner  as  described  under  the  histogenesis  of 
muscle  (p.  122). 

Blood-vessels. — The  larger  arteries  of  muscle  run  in  the  perimy- 
sium, their  general  direction  being  parallel  to  the  muscle  bundles. 
From  these,  small  branches  are  given  off  at  right  angles.     These  in 


'i     '^ 


Sarcoplasm 


,   Tendon  fibre  bundles 


Transition  zone 


y 


Sarcolemma  '  v^  -*  .  Tendon  nucleus 


Fig.  126. — Junction  of  Muscle  and  Tendon  showing  Continuity  of  Fibrils  and_Ex- 
tension  of  Sarcolemma  beyond  the  Limits  of  Cross  Striations.  Rectus  abdominis  of 
frog.     X7SO-     (Stohr.) 

turn  give  rise  to  an  anastomosing  capillary  network  with  elongated 
meshes,  which  surrounds  the  individual  muscle  fibres  on  all  sides. 
From  these  capillaries,  veins  arise  which  follow  the  arteries.  Even 
the  smallest  branches  of  these  veins  are  supphed  with  valves. 

In  tendons  blood-vessels  are  few.  They  run  mainly  in  the  con- 
nective tissue  which  surrounds  the  fibre  bundles.  Tendon  sheaths 
and  bursse,  on  the  other  hand,  are  well  supplied  with  blood-vessels. 

The  lymphatics  of  muscle  are  not  numerous.  They  accompany 
the  blood-vessels.  In  tendon  definite  lymph  vessels  are  found  only  on 
the  surface. 


THE  MUSCULAR  SYSTEM  211 

Nerves. — The  terminations  of  nerves  in  muscle  and  tendon  are 
described  under  nerve  endings  (page  434). 

TECHNIC 

(i)  A  Muscle. — Select  a  small  muscle,  human  or  animal,  and,  attaching  a 
weight  to  the  lower  end  to  keep  it  stretched,  fix  in  formahn-Miiller's  fluid  (tech- 
iiic  5,  p.  7),  and  harden  in  alcohol.  Stain  transverse  sections  with  haematoxyUn- 
picro-acid-fuchsin  (technic  3,  p.  21)  and  mount  in  balsam. 

(2)  Junction  of  Muscle  and  Tendon. — Any  muscle-tendon  junction  may  be 
selected.  Fix  in  formalin-Miiller's  fluid,  keeping  stretched  by  means  of  a  weight 
attached  to  the  lower  end.  Cut  longitudinal  sections  through  the  muscle- 
tendon  junction,  stain  with  haematoxylin-picro-acid-fuchsin,  and  mount  in  bal- 
sam. The  gastrocnemius  of  a  frog  is  convenient  on  account  of  its  small  size,  and 
because  by  bending  the  knee  over  and  tying  there,  the  muscle  can  be  easily  put 
on  the  stretch  and  kept  in  that  condition  during  fixation.  Place  the  entire  prepa- 
ration in  the  fixative  removing  the  muscle-tendon  from  the  bone  after  fixation. 


CHAPTER  V. 
GLANDS 

General  Structure  and  Classification 

Attention  was  called  in  describing  the  functional  activities  of 
cells  (page  51)  to  the  fact  that  certain  cells  possess  the  power  of  not 
only  carrying  on  the  nutritive  functions  necessary  to  maintain  their 
own  existence,  but  also  of  elaborating  certain  products  either  neces- 
sary for  the  general  body  functions  (secretions)  or  for  the  body  to 
eliminate  as  waste  (excretions) .  Such  cells  are  known  as  gland  cells 
or  glandular  epithelium,  and  an  aggregation  of  these  cells  to  form  a 
definite  structure  for  the  purpose  of  carrying  on  secretion  or  excretion 
is  known  as  a  gland. 

A  gland  may  consist  of  a  single  cell,  as,  e.g.,  the  mucous  or  goblet 
cell  on  the  free  surface  of  a  mucous  membrane  or  the  unicellular 
glands  of  invertebrates.  Such  a  cell  undergoes  certain  changes  which 
result  in  the  production  within  itself  of  a  substance  which  is  to 
be  used  outside  the  cell.  The  appearance  which  this  cell  presents 
depends  upon  the  stage  of  secretion.  It  is  thus  possible  to  differen- 
tiate between  a  "  resting' '  and  an  "  active  "  cell  or  between  an  "empty  " 
and  a  loaded"  cell.  The  mucous  secreting  cell  of  the  intestine  is 
one  of  the  simple  columnar  cells  which  constitute  the  epithelium  of  the 
mucous  membrane.  It  is  distinguishable  as  a  mucous  or  goblet  cell 
only  after  secretion  begins.  The  resting  cell  is  granular  and  takes 
a  rather  dark  cytoplasmic  stain.  As  the  cell  becomes  active,  part  of 
the  cytoplasm  is  transformed  into,  or  is  replaced  by,  a  clear  substance 
which  does  not  stain  like  cytoplasm,  but  reacts  to  hsematoxyhn. 
The  mucus  collects  first  in  the  free  end  of  the  cell,  and  gradually 
increases  in  amount  until  the  entire  cell  is  filled,  with  the  exception  of 
a  small  area  at  the  base,  where  a  little  unchanged  protoplasm  sur- 
rounds a  flattened  nucleus.  The  cell  at  this  stage  is  much  larger  than 
in  the  resting  state,  and  finally  ruptures  on  the  free  surface  and  pours 
out  its  secretion.  OpiDions  differ  as  to  the  further  behavior  of  this 
cell.  According  to  some,  its  life  history  is  now  ended,  and  its  place  is 
taken  by  other  cells  which  pass  through  the  same  process.     Others 

212 


GLANDS 


213 


believe  that  in  most  cases  the  cell  is  reconstructed  from  the  nucleus 
and  unchanged  cytoplasm,  and  again  passes  through  the  process  of 
secretion.  In  stratified  epithelium  secretion  may  begin  while  the  cell 
is  still  deeply  situated,  but  is  completed  only  as  the  cell  reaches  the 
surface,  where  its  mucus  is  to  be  discharged. 

In  describing  the  vital  properties  of  cells  (p.  50)  attention  was  called  to  the 
fact  that  all  cells  take  up  from  the  surrounding  blood  and  lymph  substances 
required  for  their  own  nutrition,  and  give  off  waste  products  (excretions).  In 
such  sense  all  cells  secrete  and  excrete.  What  distinguishes  the  gland  cell  is 
that  in  addition  to  carrying  on  its  own  metabolism  (p.  51)  it  manufactures  a 
specific  substance  not  for  its  own  use 
but  to  be  extruded  from  the  cell,  and 
used  elsewhere  in  the  body  (secretion, 
e.g.,  gastric  juice),  or  discarded  (excre- 
tion, e.g.,  urine).  Such  a  cell  takes  up 
from  blood  or  lymph  the  substances 
required,  more  or  less  completely  as- 
similates them,  and  finally  transforms 
them  into  its  specific  secretion. 

Certain  changes,  other  than  those 
described  as  seen  in  the  mucous  secret- 
ing cell,  may  occur  in  the  protoplasm 
of  actively  secreting  gland  cells.  In 
many  cells  there  appears  at  the  onset  of 
secretion  a  modification  of  the  cytoplasm 
which  has  been  designated  ergastoplasm 
(Fig.  127).  In  some  cells  the  ergasto- 
plasm takes  the  form  of  slender  threads 
near  the  base  of  ih.t  ctW,  basal  filaments, 

in  others  of  minute  rods.  Other  form  shave  been  described  as  mitochondria, 
cytosomes,  pseudochromosomes,  etc. 

Many  gland  cells  have  intracellular  secretory  canals  (see  p.  46). 

In  some  gland  cells  a  body  known  as  the  paranucleus  appears  at  the  beginning 
of  secretion.  It  is  a  rather  large,  usually  irregular  mass,  differing  somewhat  in 
staining  qualities  from  both  nucleus  and  ergastoplasm.  Its  relation  to  either 
of  these  structures,  to  the  cytoplasm,  or  to  the  secretion  is  not  known. 

The  function  of  the  nucleus  in  secretion  is  apparently  of  great  importance. 
Non-nucleated  portions  of  cells  are  probably  not  able  to  elaborate  any  true 
secretion.  When  (see  below)  the  entire  cell  enters  the  secretion  as  in  the 
mammary  gland,  the  entire  nucleus  of  course  becomes  a  part  of  the  secretion. 
In  any  event  the  onset  of  secretion  is  apt  to  be  evidenced  in  the  nucleus  by  en- 
largement and  irregularity,  in  some  cases  by  the  giving  off  of  nuclear  material 
to  the  cytoplasm,  in  others  by  amitotic  division.  According  to  some  observers 
both  ergastoplasm  and  paranucleus  arc  of  nuclear  origin. 

In  connection  with  the  mucous  cell  Cp.  212)  it  was  noted  that  according  to 
some  authorities  the  cell  dies  in  secreting,  while  others  believe  that  the  cell 


Fig.  127. — Gland  Cell  from  Pancreas  of 
Salamander;  n,  Nucleus;  cs,  caryosomes; 
pi,  plasmosomes;  cp,  paranucleus;  erg, 
ergastoplasm  filaments;  g,  secretory  gran- 
ules.    Xsoo.     (Prenant.) 


214  THE  ORGANS 

reconstructs  itself  and  can  again  secrete.  In  certain  glands,  e.g.,  the  mammary 
and  sebaceous,  the  cast  off  cells  themselves  form  the  secretion.  More  commonly 
the  cell  merely  gives  off  its  secretion,  the  remainder  of  the  cell  recovering  and 
again  goin'g  through  the  same  process. 

Most  glands  are  composed  of  more  than  one  cell,  -usually  of  a  large 
number  of  cells,  and  these  cells,  instead  of  lying  directly  upon  the  sur- 
face, Hne  more  or  less  extensive  invaginations  into  which  they  pour 
their  secretions. 

In  the  simplest  form  of  glandular  invagination  all  the  cells  lining 
the  lumen  are  secreting  cells.  In  more  highly  developed  glands  only 
the  deeper  cells  secrete,  the  remainder  of  the  gland  serving  merely  to 
carry  the  secretion  to  the  surface.  This  latter  part  is  then  known  as 
the  excretory  duct,  in  contradistinction  to  the  deeper  secreting  portion. 
In  both  the  duct  portion  and  secreting  portion  of  a  gland  the  epithe- 
lium usually  rests  upon  a  more  or  less  definite  basement  membrane  or 
membrana  propria  (page  70).  Beneath  the  basement  membrane, 
separating  and  supporting  the  glandular  elements,  is  the  connective 
tissue  of  the  gland.  This  varies  greatly  in  structure  and  quantity  in 
different  glands. 

When  the  secreting  portion  of  the  gland  is  a  tubule,  the  lumen 
of  which  is  of  fairly  uniform  diameter,  the  gland  is  known  as  a  tubular 
gland.  When  the  lumen  of  the  secreting  portion  is  dilated  in  the 
form  of  a  sac  or  alveolus,  the  gland  is  known  as  a  saccular  or  alveolar 
gland.  Intermediate  forms  have  been  described  as  tubulo-alveolar 
glands. 

A  gland  may  consist  of  a  single  tubule  or  saccule,  or  of  a  single 
system  of  ducts  leading  to  terminal  tubules  or  saccules — simple  gland. 
A  gland  may  consist  of  a  number  of  more  or  less  elaborate  duct  sys- 
tems with  their  terminal  tubules  or  saccules — compound  gland.  A 
few  glands,  e.g.,  the  thyreoid  and  thymus,  have  no  ducts,  and  are 
known  as  ductless  glands. 

All  compound  glands  are  surrounded  by  connective  tissue  which 
forms  a  more  or  less  definite  capsule.  From  the  capsule  connective- 
tissue  septa  or  trabeculce  extend  into  the  gland.  The  broadest  septa 
usually  divide  the  gland  into  a  number  of  macroscopic  compartments 
or  lobes.  Smaller  septa  from  the  capsule  and  from  the  interlobar 
septa  divide  the  lobes  into  smaller  compartments  usually  microscopic 
in  size — the  lobules.  A  lobule  is  not  only  a  definite  portion  of  the 
gland  separated  from  the  rest  of  the  gland  by  connective  tissue,  but 
represents  a  definite  grouping  of  tubules  or  alveoli  with  reference  to 


GLANDS  215 

one  or  more  terminal  ducts.  The  glandular  (epithelial)  tissue  is 
known  as  the  parenchyma  of  the  gland,  in  contradistinction  to  the 
connective  or  interstitial  tissue. 

The  relations  of  the  glandular  tissue  proper  to  the  connective  tissue  are  best 
understood  by  reference  to  development.  All  glands,  simple  and  compound, 
originate  as  simple  evaginations  from  a  surface  lined  with  epithehum.  The 
epithelial  evagination  grows  down  into  the  underlying  connective  tissue.  In  a 
compound  gland  this  invagination  tubule  becomes  the  main  excretoiy  duct.  As 
the  tubule  grows,  it  divides  and  subdivides  to  form  the  larger  and  smaller  ducts 
and  finally  the  secreting  tubules  or  alveoli.  During  the  development  of  the 
gland  tubules,  the  connective  tissue  is  also  developing,  but  is  being  largely  re- 
placed by  the  more  rapidly  growing  tubules.  The  gland  tubules  do  not  develop 
irregularly,  but  in  definite  groups,  each  group  being  dependent  upon  the  tubule 
(duct)  from  which  it  originates.  Thus  the  invagination  tubule  (main  excretory 
duct)  gives  rise  to  a  few  large  branches  (lobar  ducts),  each  one  of  which  gives 
oflf  the  subdivisions  which  constitute  a  lobe.  From  each  lobar  duct  there  arise 
within  the  lobe  a  large  number  of  smaller  branches  (lobular  ducts)  each  one  of 
which  gives  rise  to  the  subdivisions  included  in  a  lobule.  As  the  lobe  groups  and 
lobule  groups  of  tubules  develop,  the  largest  strands  of  connective  tissue  are  left 
between  adjacent  lobes  (interlobar  connective  tissue),  smaller  strands  between 
lobules  (interlobular  connective  tissue),  and  the  finest  connective  tissue  between 
the  tubules  or  alveoli  within  the  lobule  (intralobular  connective  tissue). 

Glands  may  thus  be  classified  as  follows: 
A.  Duct  glands  or  glands  of  external  secretion. 
I.  Tubular  glands. 

r  straight. 
(a)  Simple  tubular  \  coiled. 


branched. 
{h)  Compound  tubular. 
2.  Alveolar  or  saccular  glands. 
{a)  Simple  alveolar. 

{h)  Compound  alveolar,  saccular  or  racemose. 
B.  Ductless  glands  or  glands  of  internal  secretion. 

Duct  Glands 

I.  Tubular  Glands. — {a)  Simple  tubular  glands  are  simple 
tubules  which  open  on  the  surface,  their  lining  epithelium  being  con- 
tinuous with  the  surface  epithelium.  All  the  cells  may  be  secreting 
cells  or  only  the  more  deeply  situated.  In  the  latter  case  the  upper 
portion  of  the  tubule  serves  merely  as  a  duct.  In  the  more  highly 
developed  of  the  simple  tubular  glands  we  distinguish  a  mouth,  open- 


216 


THE  ORGANS 


ing  upon  the  surface,  a  neck,  usually  somewhat  constricted,  and  a 
fundus,  or  deep  secreting  portion  of  the  gland. 

Simple  tubular  glands  are  divided  according  to  the  behavior  of 
the  fundus,  into  (i)  straight,  (2)  coiled,  and  (3)  branched. 

(i)  A  straight  tubular  gland  is  one  in  which  the  entire  tubule  runs 
a  straight  unbranched  course,  e.g.,  the  glands  of  the  large  intestine 
(Fig.  128,  i). 

(2)  A  coiled  tubular  gland  is  one  in  which  the  deeper  portion  of 
the  tubule  is  coiled  or  convoluted,  e.g.,  the  sudoriferous  glands  of  the 
skin  (Fig.  128,  2). 


6 


Fig.  128. — Diagram  Illustrating  Different  Forms  of  Glands.  Upper  row,  tubidar 
glands;  i,  2,  and  3,  simple  tubular  glands;  4,  compound  tubular  gland.  Lower  row, 
alveolar  glands;  la,  2a,  and  3a,  simple  alveolar  glands;  40,  compound  alveolar  gland. 
For  description  of  la,  2a,  and  3a,  see  simple  alveolar  glands  in  text. 


(3)  A  forked  or  branched  tubular  gland  is  a  simple  tubular  gland 
in  which  the  deeper  portion  of  the  tubule  branches,  the  several 
branches  being  lined  with  secreting  cells  and  opening  into  a  superficial 
portion,  which  serves  as  a  duct.  Examples  of  slightly  forked  glands 
are  seen  in  the  cardiac  end  of  the  stomach,  and  in  the  uterus.  Other 
tubular  glands  show  much  more  extensive  branching,  the  main  duct 
giving  rise  to  a  number  of  secondary  ducts,  from  which  are  given  off 
the  terminal  tubules.  The  mucous  glands  of  the  mouth,  oesophagus, 
trachea,  and  bronchi  are  examples  of  these  more  elaborate  simple 
tubular  glands  (Fig.  128,  3). 


GLANDS  217 

(b)  Compound  tubular  glands  consist  of  a  number,  often  of  a 
large  number,  of  distinct  duct  systems.  These  open  into  a  common 
or  main  excretory  duct.  The  smaller  ducts  end  in  terminal  tubules. 
Many  of  the  largest  glands  of  the  body  are  of  this  type,  e.g.,  the  sali- 
vary glands,  Uver,  kidney,  and  testis  (Fig.  128,  4). 

In  certain  compound  tubular  glands,  as,  e.g.,  the  liver,  extensive 
anastomoses  of  the  terminal  tubules  occur.  These  are  sometimes 
called  reticular  glands. 

2.  Alveolar  Glands. — (a)  Simple  Alveolar  Glands. — The  sim- 
plest form  of  alveolar  gland  consists  of  a  single  sac  connected  with  the 
surface  by  a  constricted  portion,  the  neck,  the  whole  being  shaped  like 
a  flask  (Fig.  128,  i  a).  Such  glands  are  found  in  the  skin  of  certain 
amphibians;  they  do  not  occur  in  man.  Simple  alveolar  glands,  in 
which  there  are  several  saccules  (Fig.  128,  2  a),  are  represented  by  the 
smaller  sebaceous  glands.  Simple  branched  alveolar  glands,  in  which 
a  common  duct  gives  rise  to  a  number  of  saccules  (Fig.  128,  3  a),  are 
seen  in  the  larger  sebaceous  glands,  and  in  the  Meibomian  glands. 

(b)  Compound  Alveolar  Glands.- — These  resemble  the  com- 
pound tubular  glands  in  general  structure,  consisting  of  a  large 
number  of  duct  systems,  all  emptying  into  a  common  excretory  duct. 
The  main  duct  of  each  system  repeatedly  branches,  and  the  small 
terminal  ducts,  instead  of  ending  in  tubules  of  uniform  lumen,  as  in 
a  tubular  gland,  end  in  sac-hke  dilatations,  the  alveoli  or  acini 
(Fig.  128,  4  a).  The  best  example  of  a  compound  alveolar  gland  is 
the  mammary  gland,  although  the  lung  is  constructed  on  the  principle 
of  a  compound  alveolar  gland. 

Ductless  Glands 

Certain  structures  remain  to  be  considered  which  are  properly 
classified  as  glands,  but  in  which  during  development  the  excretory 
duct  has  disappeared.     Such  glands  are  known  as  ductless  glands. 

The  ovary  is  a  ductless  gland,  the  specific  secretion  of  which, 
the  ovum,  is  under  normal  conditions  taken  up  by  the  oviduct  and 
carried  to  the  uterus.     This  is  known  as  a  dehiscent  gland. 

Other  ductless  glands,  such  as  the  thyreoid,  hypophysis  and 
adrenal,  are  known  as  glands  of  internal  secretion,  their  specific 
secretions  passing  directly  into  the  blood  or  lymph  systems. 

A  few  glands,  e.g.,  the  liver  and  pancreas,  have  both  an  internal 
secretion,  and  an  external  secretion. 


218  THE  ORGANS 

General  Structtire  of  Mucous  Membranes 

The  alimentary  tract,  the  respiratory  tubules,  parts  of  the  genito- 
urinary system,  and  some  of  the  organs  of  special  sense  are  lined  by 
mucous  membranes.  While  differing  as  to  details  in  different  organs, 
the  general  structure  of  all  mucous  membranes  is  similar.  The 
essential  parts  are  (i)  surface  epitheUum,  (2)  basement  membrane, 
and  (3)  stroma  or  tunica  propria.  The  epithelium  may  be  simple 
columnar,  as  in  the  gastro-intestinal  canal;  ciHated,  as  in  the  bronchi; 
stratified  squamous,  as  in  the  oesophagus,  etc.  The  epithelium  rests 
upon  a  basement  membrane  or  membrana  propria  which,  Hke  the  same 
membrane  in  glands,  is  described  by  some  as  a  product  of  the  epithe- 
Uum, by  others  as  a  modification  of  the  underlying  connective  tissue. 
Beneath  the  basement  membrane  is  a  connective- tissue  stroma,  or 
tunica  propria.  This  usually  consists  of  loosely  arranged  fibrous 
tissue  with  some  elastic  fibres.  It  may  contain  smooth  muscle  cells 
and  lymphoid  tissue. 

In  addition  to  the  three  layers  above  described  there  is  frequently 
a  fourth  layer  between  the  stroma  and  the  underlying  connective 
tissue.  This  consists  of  one  or  more  layers  of  smooth  muscle,  and 
is  known  as  the  muscularis  mucosce. 

A  mucous  membrane  usually  rests  upon  a  layer  of  connective 
tissue  rich  in  blood-vessels,  lymphatics,  and  nerves — the  submucosa. 


CHAPTER  VI 

THE  DIGESTIVE  SYSTEM 

The  digestive  system  consists  of  the  alimentary  tract  and  certain 
associated  structures  such  as  glands,  teeth,  etc. 

The  alimentary  tract'is  a  tube  extending  from  lips  to  anus.  Dif- 
ferent parts  of  the  tube  present  modifications  both  as  to  caHbre  and 
as  to  structure  of  wall. 

The  embryological  subdivision  of  the  canal  into  headgut,  foregut, 
midgut,  and  endgut  admits  of  further  subdivision  upon  an  anatomical 
basis  as  follows: 

I.  Headgut:  (a)  Mouth,  including  the  tongue  and  teeth. 

(b)  Pharynx. 

II.  Foregut:    (a)  (Esophagus. 

(b)  Stomach. 

III.  Midgut:  Small  intestine. 

IV.  Endgut:     (a)  Large  intestine. 

(b)  Rectum. 

The  entire  canal  is  lined  by  mucous  membrane,  the  modifications 
of  which  constitute  the  most  essential  difference  in  structure  of  its 
several  subdivisions. 

Beneath  the  mucosa  is  usually  more  or  less  connective  tissue, 
which  in  a  large  portion  of  the  canal  forms  a  definite  submucosa. 

Muscular  tissue  is  present  beneath  the  submucosa  throughout  the 
greater  part  of  the  canal.  In  most  regions  it  forms  a  definite,  con- 
tinuous, muscular  tunic. 

The  upper  and  lower  ends  of  the  tube — mouth,  pharynx,  oesoph- 
agus, and  rectum — are  quite  firmly  attached  by  fibrous  tisue  to  the 
surrounding  structures.  The  remainder  of  the  tube  is  less  firmly 
attached,  lying  coiled  in  the  abdominal  cavity,  its  surface  covered, 
except  along  its  attached  border,  by  a  serous  membrane,  the  visceral 
peritoneum. 

219 


220  THE  ORGANS 

I.  THE  HEADGUT 

The  Mouth 

The  Mucous  Membrane  of  the  Mouth. — This  consists  of 
stratified  squamous  epithelium  lying  upon  a  connective- tissue  stroma 
or  tunica  propria.  The  latter  is  thrown  up  into  papillcs,  which  do 
not,  however,  appear  upon  the  free  surface  of  the  epithehum.  The 
submucosa  is  a  firm  connective- tissue  layer  with  few  elastic  fibres. 
The  thickness  of  the  epithehum,  the  character  of  the  strom.a,  and  the 
height  of  the  papillae  vary  in  different  parts  of  the  mouth.  There  is 
no  muscularis  mucosae. 

At  the  junction  of  the  skin  and  m.ucous  membrane  (red  margin  of 
the  Hps)  the  epitheHal  layer  is  much  thickened,  the  stroma  is  thinned, 
and  the  papillae  are  very  high.  At  this  point  the  stratum  corneum 
of  the  skin  passes  over  into  the  softer  nucleated  epithelium  of  the 
mouth,  while  the  stratum  lucidum  and  stratum  granulosum  of  the 
skin  terminate  (see  skin,  page  383). 

The  mucous  m.embrane  of  the  gums  has  prominent,  long, 
slender  papillae,  the  sum.mits  of  which  are  covered  by  a  very  thin 
layer  of  epithehum.  This  nearness  of  the  vascular  stroma  to  the 
surface  accounts  for  the  ease  with  which  the  gums  bleed.  That 
portion  of  the  gums  which  extends  over  the  teeth  is  devoid  of  papil- 
lae. The  submucosa  of  the  gums  is  firmly  attached  to  the  underlying 
periosteum. 

The  mucous  membrane  fining  the  cheeks  has  low,  small  papillae, 
and  the  submucosa  is  closely  adherent  to  the  muscular  fibres  of  the 
buccinator. 

Covering  the  hard  palate,  the  mucous  membrane  is  thin  and  the 
short  papillse  are  obHquely  placed,  their  apices  being  directed  ante- 
riorly.    The  submucosa  is  firmly  attached  to  the  periosteum. 

Over  the  soft  palate  the  papillae  of  the  mucous  membrane  are  low 
or  even  absent.  They  are  somewhat  higher  on  the  uvula,  the  pos- 
terior surface  of  which  shows  a  transitional  condition  of  its  epithe- 
hum, areas  of  stratified  squamous  alternating  with  areas  of  stratified 
columnar  cihated  epithehum.  Throughout  the  mucous  membrane  of 
the  soft  palate,  uvula,  and  fauces,  the  stroma  and  subm.ucosa  contain 
diffuse  lymphatic  tissue.  In  some  places  the  lymphoid  cells  are  so 
closely  placed  as  to  form  distinct  nodules. 

Glands  of  the  Oral  Mucosa.^^ — Distributed  throughout  the 

^  For  description  of  the  larger  salivary  glands  see  page  276. 


THE  DIGESTIVE  SYSTEM  221 

oral  mucosa  are  small  branched  tubular  glands.  Only  in  those  parts 
of  the  mucous  membrane  which  are  closely  attached  to  underlying 
bone,  as  on  the  gums  and  hard  palate,  are  mucous  glands  few  or 
entirely  absent.  While  the  deeper  portions  of  the  glands  are  in  the 
submucosa,  some  of  the  tubules  usually  he  in  the  stroma  of  the  mucous 
membrane. 

The  ducts  open  upon  the  surface  and  are  hned  with  a  continuation 
of  the  surface  stratified  squamous  epithehum  as  far  as  the  first  bifur- 
cation. Here  the  epithelium  becomes  stratified  columnar,  and  this, 
as  the  smaller  branches  are  approached,  passes  over  into  the  simple 
columnar  type.  Not  infrequently  ducts  of  small  secondary  glands 
empty  into  the  main  duct  during  its  passage  through  the  mucosa. 

According  to  the  character  of  their  secretions,  the  oral  glands  are 
divided  into : 

(a)  Mucous  glands,  which  secrete  a  mucin-containing  fluid 
(mucus) ; 

{h)  Serous  glands,  which  secrete  a  serous  (albuminous)  fluid; 

(c)  Mixed  glands,  the  secretion  of  which  is  partly  mucous  and 
partly  serous. 

Morphologically,  also,  a  similar  distinction  can  be  made  in  regard 
to  the  glandular  epithehum  which  lines  the  terminal  tubules,  the 
tubules  of  mucous  glands  being  hned  with  "mucous"  cells,  those  of 
serous  glands  with  "serous  cells,"  while  of  the  mixed  glands  the  cells 
of  some  tubules  are  mucous,  of  others  serous.  In  certain  tubules 
both  mucous  and  serous  cehs  occur.  Th%  appearance  which  these 
cells  present  depends  largely  upon  their  secretory  condition  at  the 
time  of  death. 

Serous  cells  when  resting  have  a  shghtly  granular  protoplasm, 
which  in  the  fresh  condition  is  highly  refractive,  giving  the  cells  a 
transparent  appearance.  With  the  beginning  of  secretion  the  gran- 
ules increase  in  number  and  the  cehs  become  darker.  Stained  with 
hacmatoxyUn-eosin,  serous  tubules  have  a  purphsh  color.  The  nuclei 
are  spherical  or  oval,  and  are  situated  between  the  centre  and  base 
of  the  cell  (Fig.  i8i,  p.  279). 

Mucous  cells  are  in  the  quiescent  state  rather  small  cuboidal  or 
pyramidal  colls,  with  cloudy  cytoplasm  and  nuclei  situated  at  the 
base  of  the  cell.  When  active  the  mucous  cells  are  much  larger, 
with  clear  cytoplasm  and  with  nuclei  flattened  against  the  basement 
membrane.  The  protoj)lasm  of  the  fresh  unstained  mucous  cell  is 
less  highly  refractive  than  that  of  the  serous  cell.     It  consequently 


222  THE  ORGANS 

appears  darker  and  less  transparent.  Mucous  tubules  are  larger 
and  more  irregular  in  shape  than  serous  tubules,  and  when  stained 
with  haematoxylin-eosin  either  remain  almost  wholly  unstained  or 
take  a  pale  blue  hsematoxylin  stain  (Fig.  i8i,  p.  279).  Many 
mucous  tubules  have  in  addition  to  the  mucous  cells  a  peculiar,  often 
crescentic-shaped  group  of  cells  on  one  side  of  the  tubule,  between 
the  mucous  cells  and  the  basement  membrane.  These  cells  are 
granular  and  stain  very  much  Uke  serous  cells  with  haematoxyhn- 
eosin,  thus  resembling  the  latter  in  appearance.  On  account  of  the 
shape  of  the  groups,  they  are  known  as  the  crescents  of  Gianuzzi  or 
demilunes  of  Heidenhain  (Fig.  181,  p.  279).  The  cells  of  the  crescents 
are  connected  with  the  lumen  by  means  of  secretory  canals,  which 
pass  between  the  mucous  cells  and  end  in  branches  within  the  proto- 
plasm of  the  crescent  cells.  It  is  quite  possible  that  some  of  the 
crescents  are  not  serous  cells  but  mucous  cells  in  the  non-active 
condition  which  have  been  pushed  away  from  the  lumen  by  the  more 
active  cells.  Such  cell  groups  are  not  connected  with  the  lumen  of 
the  gland  by  intercellular  secretory  canals. 

Peculiar  irregular  branching  cells  have  been  described,  extending 
from  the  basement  membrane  in  between  the  mucous  cells.  They 
are  known  as  "basket"  cells  and  are  supposed  to  be  supportive  in 
character. 

The  cells  of  both  mucous  and  serous  tubules  rest  upon  a  membrana 
propria,  outside  of  which,  separating  the  tubules,  is  a  cellular  connect- 
ive-tissue stroma. 

Of  the  small  glands  of  the  mouth,  a  group  near  the  root  of  the 
tongue  are  of  the  mucous  variety,  some  "lingual"  glands  in  the  region 
of  the  circumvallate  papillae  are  serous,  while  the  remainder  are  of 
the  mixed  type. 

Blood-vessels. — The  larger  vessels  run  mainly  in  the  submucosa. 
The  arteries  of  the  submucosa  give  off  one  group  of  branches  to  the 
tunica  propria,  where  they  break  up  into  a  dense  subepithelial  capil- 
lary network,  sending  capillary  loops  into  the  papillae.  A  second 
group  of  arterial  branches  pass  to  the  submucosa,  where  they  give 
rise  to  capillary  networks  among  the  tubules  of  the  mucous  glands. 
From  the  capillaries  veins  arise  which  accompany  the  arteries. 

Lymphatics. — The  larger  lymph  vessels  he  in  the  submucosa. 
These  send  smaller  branches  into  the  tunica  propria,  where  they  open 
into  small  lymph  capillaries  and  spaces. 

Nerves. — MeduUated  nerve  fibres  form  plexuses  in  the  submucosa 


THE  DIGESTIVE  SYSTEM  223 

and  deeper  parts  of  the  mucosa.  From  these  plexuses,  branches  are 
given  off  which  lose  their  medullary  sheaths  and  form  a  second 
plexus  of  non-medullated  fibres  just  beneath  the  epithelium.  From 
this  subepithelial  plexus,  branches  pass  in  between  the  epithehal 
cells  to  terminate  in  end  brushes  or  in  tactile  corpuscles.  The 
nerves  belong  to  the  cerebro-spinal  system,  and  are  dendrites  of 
sensory  ganglion  cells.  Axones  of  sympathetic  neurones  are  also 
present  in  the  oral  mucosa,  destined  mainly  for  the  muscle-tissue  of 
the  blood-vessels. 

TECHNIC 

(i)  The  superficial  cells  of  the  oral  mucous  membrane  may  be  prepared  for 
examination  as  in  technic  i,  page  63. 

(2)  For  the  study  of  the  mucous  membrane  of  different  parts  of  the  mouth, 
fix  smaU  pieces  in  formalin-Miiller's  fluid  (technic  5,  p.  7),  cut  sections  perpen- 
dicular to  the  surface,  stain  with  haematoxylin-eosin  (technic  i,  p.  20),  and  mount 
in  balsam. 

(3)  Small  mucous  and  serous  glands  of  the  mouth  may  be  studied  in  the 
preceding  sections. 

The  Tongue 

The  tongue  is  composed  mainly  of  striated  muscle  fibres,  sup- 
ported by  connective  tissue  and  covered  by  a  mucous  membrane. 


Fungiform 
papillae 


Fig.   129. — Surface  View  of  Tongue  showing  filiform   |),ii)ill;e  and   <!irtc    fungiform 

papilla:  (Spallcholz). 

While   the  bundles  of  fibres  interlace  in  all  directions,  three  fairly 
distinct  planes  can  be  differentiated. 


224 


THE  ORGANS 


(i)  Vertical  and  somewhat  radiating  fibres — hyoglossus,  genio- 
glossus,  and  vertical  fibres  of  the  lingualis. 

(2)  Transverse  fibres — transverse  fibres  of  the  lingualis. 

(3)  Longitudinal  fibres — the  styloglossus  and  longitudinal  (supe- 
rior and  inferior)  fibres  of  the  lingualis. 

The  connective  tissue  which  supports  the  muscle  fibres  and  sepa- 
rates them  into  bundles  contains  mucous  glands  and  fat.  A  strong 
band  of  connective  tissue,  the  septum  linguce,  extends  lengthwise 
through  the  middle  of  the  tongue,  dividing  it  into  right  and  left  halves. 

The  submucosa  of  the  tongue  is  not  well  developed,  the  stroma  of 
the  mucosa  resting  directly  upon  the  underlying  muscle. 


Fig.  130. — Vertical  Section  through  Two  Filiform  Papillae  from  Human  Tongue. 
X80.  (Szymonowicz.)  a,  Horny  epithelium;  b,  stroma;  c,  epithelium;  d,  secondary 
papilla. 


The  mucous  membrane  of  the  tongue  resembles  that  of  the  mouth, 
but  dffers  from  the  latter  in  that  in  addition  to  the  low  papillae, 
such  ais  are  found  in  the  oral  mucosa,  the  upper  surface  of  the  tongue 
is  studded  with  numerous  and  much  larger  papillae  or  villi.  These 
project  from  the  surface  and  give  to  the  tongue  its  characteristic 
roughness.  Three  forms  of  papillae  are  distinguished: — Filiform, 
fungiform,  and  circumvallate. 


THE  DIGESTIVE  SYSTEM  225 

(i)  Filiform  Papillae  (Fig.  130). — These  are  the  most  numerous 
and  are  distributed  over  the  entire  dorsum  of  the  organ.  Each 
consists  of  a  central  core  of  connective  tissue  containing  elastic  fibres, 
which  is  long  and  slender,  and  is  covered  by  stratified  squamous 
epithehum.  From  the  summit  of  each  papilla  are  given  off  several 
secondary  papillce.  The  epithelium  covering  the  papillae  is  hornified 
and  often  extends  from  the  surface  as  a  long  thread-like  projection — 
hence  the  name,  filiform. 


^:^:M-\,. 


—    b 


Fig.  131. — Vertical  Section  through  Fuagiform  Papilla  of  Human  Tongue.     X45. 
(Szyraonowicz.)     a,  Secondary  papilla;  b,  epithelium;  c,  muscle  fibres. 

(2)  Fungiform  Papilla  (Fig.  131)- — Scattered  irregularly  over 
the  entire  dorsum  among  the  filiform  papillae,  but  fewer  in  number, 
are  larger  papilla;  of  somewhat  different  structure  known  as  fungi- 
form papillae.  Their  summits  are  rounded  instead  of  pointed  and 
their  bases  are  narrowed.  Secondary  papillae  are  given  off  not  only 
from  the  summit,  but  from  the  sides  of  the  papilla.  The  epithelial 
covering  is  comparatively  thin  and  is  not  hornified.  The  connective- 
tissue  core  of  these  papillae  contains  but  few  elastic  fibres. 

(3)  The  Circumvallate  Papilla  fp^ig.  132). — These  are  from 
nine  to  fifteen  in  number,  and  are  grouped  on  the  posterior  surface 
of  the  dorsum  of  the  tongue.     They  resemble  the  fungiform  papillae, 

^  but  are  much  larger.     Each  lies  rather  deep  in  the  mucous  membrane, 

15 


226 


THE  ORGANS 


Surrounded  by  a  groove  or  trench  and  wall  (whence  the  name  circum- 
vallate) .  The  wall  is  somewhat  lower  than  the  papilla,  thus  allowing 
the  latter  to  project  slightly  above  the  surface.  Secondary  papillae 
are  confined  to  the  upper  surface  of  the  papilla,  the  sides  being  free 
from  secondary  papillae.  The  surface  of  the  papilla  and  the  borders 
of  the  groove  and  wall  are  covered  by  stratified  squamous  epithelium. 
Lying  in  the  epithelium  of  the  side  wall  and  sometim.es  of  the  opposite 
trench  wall  are  oval  bodies,  the  so-called  taste  buds,  which  serve  as 


gfc*.. 


•^X" 


^^j^ 


^^arc^c 


Fig.  i32.-^Vertical  Section  through  a  Circumvallate  Papilla  of  Human  Tongue. 
X37.  (Szymonowicz.)  a,  Secondary  papilla;  b,  wall;  c,  trench;  d,  epithelium  of 
tongue;  e,  stroma;  /,  submucosa;  g,  Ebner's  glands. 


organs  for  the  nerves  of  taste  (see  nervous  system) .  Into  the  trench 
surrounding  the  circumvallate  papilla  open  the  ducts  of  serous  glands 
(Ebner's  glands). 

The  lymph  follicles  of  the  tongue  have  been  already  described 
(page  180)  under  the  head  of  the  lingual  tonsils. 

For  glands  of  the  tongue  see  page  222. 

The  larger  blood-vessels  run  in  the  connective-tissue  septa. 
These  give  off  smaller  branches,  which  break  up  into  capillary  net- 
works surrounding  the  muscle  fibres  and  forming  a  plexus  just  be- 
neath the  epithehum.  From  the  latter  are  given  off  capillaries  to 
the  papillae.  The  capillaries  converge  to  form  veins,  which  iii  general 
follow  the  course  of  the  arteries. 


THE  DIGESTIVE  SYSTEM  227 

Fine  lymph  spaces  occur  in  the  papilte  and  open  into  a  plexus  of 
small  lymph  capillaries  just  beneath  the  papillae.  These  communi- 
cate with  a  deeper  plexus  of  larger  lymphatics,  which  increase  in  size 
and  number  as  they  pass  backward  and  form  an  especially  dense 
lymphatic  network  at  the  root  of  the  tongue  in  the  region  of  the 
lingual  tonsils. 

Nerves.— Sympathetic  fibres  pass  mainly  to  the  smooth  muscle 
of  the  blood-vessels  and  to  the  glands.  Medullated  motor  nerve 
fibres  supply  the  hngual  muscles.  Medullated  sensory  nerves  in- 
clude those  of  the  special  sense  of  taste  as  well  as  those  of  ordinary 
sensation.^  They  end  freely  among  the  epithehal  cells  or  in  con- 
nection with  special  end-organs— the  taste  buds  mainly  in  the  circum- 
vallate  papilLT,  and  the  end-bulbs  of  Krause  in  the  fungiform  papilte. 

TECHNIC 

Remove  pieces  of  the  dorsum  of  the  tongue,  selecting  parts  that  will  include 
the  diflferent  forms  of  papiUae  and  cutting  well  into  the  underlying  muscular 
tissue.  Treat  as  in  technic  2,  p.  223,  or  sections  may  be  stained  with  h^matoxy- 
lin-picro-acid-fuchsin  (technic  3,  p.  21). 

In  sections  from  the  back  part  of  the  tongue  good  examples  of  mucous  and 
serous  glands  are  usually  found. 

In  small  sections  of  the  tongue  the  muscle  fibres  are  seen  arranged  in  bundles, 
surrounded  by  connective  tissue  and  interlacing  in  all  directions.  For  the  study 
of  the  arrangement  of  the  different  planes  of  muscle,  complete  transverse  sec- 
tions should  be  made  at  intervals  through  the  entire  tongue.  The  muscle  and 
connective-tissue  relations  are  best  brought  out  by  the  ha^matoxylin-picro-acid- 
fuchsin  stain. 


The  Teeth 

A  tooth  is  a  hard  bone-like  structure,  part  of  which  projects  above 
the  surface  of  the  jaw  as  the  crown,  while  the  deeper  portion,  the  root 
or  fang,  is  buried  in  a  socket  of  the  alveolar  margin  (Fig.  133).  The 
junction  of  the  root  and  crown  is  known  as  the  neck. 

A  tooth  consists  of  a  soft  central  core,  the  ptdp  cavity,  surrounded 
by  dentine  (Figs.  133  and  135).  The  latter  constitutes  the  main  bulk 
of  the  tooth.  The  exposed  portion  of  the  dentine  is  covered  by  a  thin 
layer  of  extremely  hard  substance,  the  enamel  (Fig.  133,  i),  while  the 
alveolar  portion  of  the  dentine  is  covered  with  cemcntum  (Fig.  13^,  3). 
Of  these  the  dentine  and  cementum  are  of  connective- tissue  origin, 
the  enamel  of  epithelial. 


228 


THE  ORGANS 


The  pulp  cavity  occupies  the  central  axis  of  the  tooth  (Figs.  133 
and  135).  In  the  root  it  is  known  as  the  root  canal.  At  the  apex  of 
the  root  it  communicates  with  the  underlying  tissue  by  means  of  one 
■or  more  minute  apical  foramina,  through  which  blood-vessels  and 
nerves  enter  the  pulp  cavity. 

The  dental  pulp  consists  of  loose  connective  tissue  approaching  the 
embryonal  in  type,  composed  of  many  fusiform  and  stellate  cells  and 

delicate  white  fibrils.  There  are  ap- 
parently no  elastic  fibres.  A  few 
smooth  muscle  cells  have  been  de- 
scribed. The  pulp  is  richly  suppHed 
with  blood-vessels  and  nerves  which 
are  found  only  in  this  part  of  the 
tooth.  Along  the  dentinal  surface  of 
the  pulp  the  connective- tissue  cells 
are  arranged  as  a  single  layer  of 
columnar  cells,  the  odontoblasts. 
These  cells  are  closely  alUed  to 
osteoblasts.  Their  nuclei  lie  toward 
their  inner  ends.  Each  cell  sends 
out  an  inner  process,  which  is  usually 
single  and  passes  into  the  dental  pulp, 
several  lateral  processes  which  inter- 
lace with  and  probably  anastomose 
with  similar  processes  from  other 
cells,  and  one  or  more  outer  fibre- 
hke  processes  which  enter  the  den- 
tine, where  they  form  the  dentinal 
fibres.  These  frequently  extend  en- 
tirely through  the  dentine.  Just 
beneath  the  layer  of  odontoblasts, 
the  connective-tissue  cells  are  much 
fewer  in  number  than  in  the  rest  of 
the  dental  pulp.  Appearing  in  sec- 
tions as  a  clear  band,  it  is  known  as  the  layer  of  Weil.  Immediately 
internal  to  the  layer  of  Weil,  the  cells  are  more  closely  arranged  than 
elsewhere  in  the  pulp. 

Dentine  (Figs.  135  and  136,  D)  is  somewhat  harder  than  bone 
which  it  resembles  in  structure.  According  to  von  Bibra  its  chemical 
composition  is: 


Fig.  133. — Vertical  Section  of 
Tooth,  in  siiu.  X15.  (Waldeyer.) 
c,  Pulp  cavity,  the  letter  being  at 
about  the  junction  of  crown  and 
root;  I,  enamel  showing  radial  and 
longitudinal  markings;  2,  dentine 
showing  dental  canals;  3,  cementum 
(containing  bone  corpuscles) ;  4,  peri- 
dental membrane;  5,  bone  of  lower 
jaw. 


THE  DIGESTIVE  SYSTEM 


229 


Flo.   134. — Diiigram  of  Section  throiij^h  an  Incisor,  showinR  lilood-vosscls 
and  I'cridcnlai  Mcmljrane.     (Xoycs.) 


230  THE  ORGANS 

Organic  matter,  28 .  01 

Calcium  phosphate  and  fluorid,  66.72 

Calcium  carbonate,  3.36 

Magnesium  phosphate,  i .  18 

Other  salts,  o.  73 

Dentine  constitutes  the  bulk  of  the  tooth  and  is  peculiar  in  that 
it  contains  canaliculi,  dentinal  canals  (Figs.  135  and  136,  Dk),  but 
no  lacunae  or  bone  cells.     The  latter  are  represented  by  the  odonto- 


id 


i' 


4^*  -^-  .  ,  -%^-?^v%^ 


/*^' 


^^'^ 


*.* 


^» 


^^^ 


^,?'. 


Fig.  135. — Cross  Section  through  Root  of  Human.  Canine  Tooth  (X25)  (Sobotta), 
showing  relations  of  pulp  cavity,  dentine,  and  cementum.  P,  Pulp  cavity;  D,  dentine; 
C,  cementum;  K,  Tomes'  granular  layer. 

blasts  of  the  pulp,  which,  as  already  noted,  lie  at  the  inner  side  of  the 
dentine,  into  the  canaHculi  of  which  they  send  the  dentinal  fibres. 
Dentine  is  non-vascular.  The  dentinal  canals  begin  at  the  dental 
pulp,  into  which  they  open  and  where  they  have  a  calibre  of  2  to  5/^. 
They  pass  outward  radially,  to  the  limit  of  the  dentine,  and,  while 
taking  different  directions  in  different  parts  of  the  dentine,  are  essen- 


THE  DIGESTIVE  SYSTEM 


231 


tially  parallel.  In  their  passage  through  the  dentine  the  dentinal 
canals  describe  two  series  of  curves,  known  as  primary  and  secondary 
curves.  The  former  take  the  form  of  an  elongated  S  from  pulp  to 
enamel  or  cementum,  the  secondary  curves  are  twistings  of  the  canals 
(drawn  out  corkscrew).  These  twistings  are  very  fine  as  many  as 
200  turns  having  been  described  in  the  length  of  a  canal.  In  their 
passage  through  the  dentine  the  main  canals  gradually  grow  smaller 
until  their  diameter  is  from  0.5  to  in.  They  give  off  minute  side 
branches  from  0.3  to  o.6/«  in  diameter,  which  leave  the  main  tubules 


KH 


Dk 


c 


K 


D 


Fig.  136. — From  Lon^iludinal  Section  through  Root  of  Human  Molar  Tooth 
(X2oo)  (.Sobottaj,  showing  junction  of  dentine  and  cementum.  C,  Cementum;  D, 
dentine;  K,  Tomes'  granular  layer;  Dk,  dental  canals:  KH,  lacunae  of  cementum. 

at  almost  right  angles,  but  soon  turn  slightly  outward.  They  anasto- 
mose with  similar  branches  from  other  canals.  This  anastomosis  takes 
place  not  only  between  branches  of  adjacent  canals,  but  also  between 
branches  of  canals  some  distance  apart.  The  main  canals  terminate 
either  in  blind  extremities,  or  form  loops  by  anastomosing  with  neigh- 
boring tubules.  Some  of  the  tubules  have  quite  extensive  terminal 
branchings,  other  tubules  have  only  two  or  three  end  branches.  A 
few  tubules  run  slightly  beyond  the  limits  of  the  dentine  into  the 
enamel.  The  arrangement  of  the  dentinal  canals  and  their  branches 
differs  in  different  parts  of  the  tooth.  In  the  crown  there  are  few 
large  branches  and  the  main  canals  show  distinct  ])rimary  and  second- 
ary curves,  most  of  them   ending  bh'ndly  in   brush-like   branchings 


232  THE  ORGANS 

just  under  the  enamel,  but  some  continuing  over  into  the  enamel  for 
from  lo  to  4.o/«,  where  they  lie  in  the  cement  between  the  prisms. 
In  the  root  the  canals  have  an  almost  straight  direction  (without 
primary  curves).  Large  branches  are  more  numerous  and  the  main 
canals  have  a  somewhat  more  irregular  arrangement.  They  probably 
do  not  pass  over  into  the  cementum,  but  end  at  the  granular  layer. 
The  dentine  immediately  around  a  dentinal  canal  is  more  dense  and 
harder  than  elsewhere  and  forms  a  sort  of  sheath  for  the  canal— 
Neumann's  dental  sheath.  Between  the  dentinal  canals  is  a  calcified 
ground  substance,  in  which  are  connective-tissue  fibres  running  in  a 
direction  parallel  to  the  surface  of  the  pulp,  this  corresponding,  as  in 
bone,  to  the  deposition  of  the  dentine  in  successive  layers.  In  a  longi- 
tudinal section  of  the  dentine  of  the  crown,  lines  are  seen  running 
parallel  to  the  surface  of  the  pulp.  They  are  known  as  the  lines  of 
Schreger  and  are  probably  due  to  irregularities  in  deposition  of  the 
dentine. 

Spaces  which  probably  represent  incomplete  calcification  of  the 
dentine  occur  in  the  peripheral  portion  of  the  dentine  of  the  crown. 
These  are  known  as  interglobular  spaces  (Fig.  137,  Jg).  They  are 
filled  with  a  substance  resembling  uncalcified  dentine.  The  inter- 
globular spaces  do  not  interrupt  the  dental  canals  which  pass  through 
them  with  no  break  in  their  continuity. 

In  the  outer  part  of  the  dentine  of  the  root  are  similar  spaces  which 
are  smaller  and  more  closely  placed.  These  form  the  so-called 
Tomes'  granular  layer  (Fig.  136,  K).  In  the  root  of  the  tooth  this 
layer  is  quite  thick,  separating  the  cementum  from  the  dentine.  Its 
spaces  or  lacunae  send  off  tiny  canaliculi  which  run  in  all  directions  and 
anastomose  with  one  another,  with  the  dentinal  tubules,  and  with  the 
lacunae  of  the  cementum.  This  layer,  with  its  small  closely  placed 
spaces  and  fine  irregularly  running  canaliculi,  contrasts  sharply  on  the 
one  side  (Fig.  136)  with  the  dentine  and  its  straight  parallel  tubules; 
and  on  the  other  side,  with  the  cementum  and  its  large  and  more 
widely  separated  lacunae.  Over  the  crown  of  the  tooth  this  layer  is 
much  thinner  and  as  the  apex  is  approached,  becomes  lost  completely, 
the  dental  tubules  extending  to,  and  some  of  them  entering  slightly, 
(see  above)  the  enamel.^ 

^Distinction  is  sometimes  made  between  primary  and  secondary  dentine.  Primary 
dentine  is  that  dentine  normally  formed  during  the  development  of  a  tooth  and  corre- 
sponds to  the  description  given,  later  under  some  stimulus,  e.g.,  excessive  wear,  for- 
mation of  dentine  again  takes  place,  in  which  case  the  canals  are  often  much  more  ir- 
regularly arranged;  this  is  known  as  secondary  dentine. 


THE  DIGESTIVE  SYSTEM  233 

The  ENAMEL  covers  the  exposed  part  or  crown  of  the  tooth  and  is 
the  hardest  substance  in  the  body.  It  is  thickest  over  the  crown  and 
gradually  decreases  in  thickness  along  the  sides  of  the  tooth  until  it 
reaches  the  neck  where  it  stops.  It  contains  little  more  than  a  trace 
of  organic  substance,  its  chemical  composition  being,  according  to  von 
Bibra: 

Organic  matter,  3 .  59 

Calcium  phosphate  and  fluoric!,  89.82 

Calcium  carbonate,  4-37 

Magnesium  phosphate,  i .  34 

Other  salts,  0.88 

It  consists  of  long  six-sided  prisms  3  to  6/«  in  diameter — enamel  fibres 
or  enamel  prisms  (Fig.  137,  Sp) — which  take  a  slightly  wavy  course 
through  the  entire  thickness  of  the  enamel.  The  prisms  are  attached 
to  one  another  by  a  small  amount  of  cement  substance,  and  are 
grouped  into  bundles,  the  prisms  of  each  bundle  being  parallel,  but 
the  bundles  themselves  frequently  crossing  one  another  at  acute 
angles.  In  the  human  adult  the  prisms  are  homogeneous;  in  the  em- 
bryo they  show  a  longitudinal  fibrillation.  Rather  indistinct  parallel 
lines  (the  lines  of  Retzius)  cross  the  enamel  prisms.  They  probably 
represent  the  deposition  in  layers  of  the  Ume  salts,  although  they  are 
considered  by  some  as  artefacts.  The  enamel  is  covered  by  an  appar- 
ently structureless  membrane,  the  cuticula  dentis. 

The  CEMENTUM  (Fig.  136,  C)  covers  the  dentine  of  the  root  in  a 
manner  similar  to  that  in  which  the  enamel  covers  the  dentine  of  the 
crown  (Fig.  133,  i  and  3).  It  forms  a  thin  layer  at  the  neck,  but  in- 
creases in  thickness  as  the  deeper  part  of  the  root  is  reached.  Cemen- 
tum  is  bone  tissue.  It  contains  lacunae  and  bone  cells.  These  vary  much 
more  in  size  and  shape  than  do  those  of  bone,  are  very  irregularly 
distributed  and  may  be  absent  from  considerable  areas.  From  the 
lacunae  radiate  canalicuh,  but  there  is  no  distinct  lamellation  and  no 
Haversian  systems  or  blood-vessels,  excepting  in  the  large  teeth  of  the 
larger  mammalia,  and  in  the  teeth  of  the  aged,  where  they  may  be 
present.  Channels,  similar  to  Volkmann's  canals  in  bone,  not  sur- 
rounded by  concentric  lamelke,  but  serving  for  the  passage  of  blood- 
vessels, are  quite  frequent  in  the  thicker  portions  of  the  cementum. 
The  ground  substance  of  the  cementum  is  continuous  with  that  of 
the  dentine  and  many  canaliculi  of  the  former  o])en  into  the  inter- 
globular spaces  of  the  latter.  Many  uncalcilicd  Shari)ey's  llbres 
penetrate  the  cementum. 


234 


THE  ORGx\NS 


The  Peridental  Membrane. — Surrounding  the  root  of  the  tooth  and  filling 
in  the  space  between  it  and  the  wall  of  the  alveolus  is  a  layer  of  connective 
tissue  which  is  known  as  the  peridental  membrane  (Fig.  134).  It  attaches  the 
tooth  to  the  alveolus,  attaches  the  teeth  to  each  other,  supports  the  free  margin 
of  the  gum  and  holds  it  to  the  tooth,  and  serves  for  the  transmission  of  vessels 
and  nerves.  It  consists  of  dense  white  fibrous  tissue  with  few  or  no  elastic 
fibres.  In  general  it  resembles  periosteum  and  has  been  described  as  a  reflec- 
tion of  the  alveolar  periosteum  upon  the  root  of  the  tooth.  The  fibres  fall  into 
two  classes,  long  fibres  which  pass  from  the  cementum  to  the  coarser  connective 


Dk 


>k 


5 

Fig.  137. — From  Longitudinal  Section  of  Crown  of  Human  Premolar  (X200) 
(Sobotta),  showing  junction  of  enamel  and  dentine.  S,  Enamel;  D,  dentine;  Sp,  enamel 
prisms;  Dk,  dental  canals;  Jg,  interglobular  spaces.  A  few  dentinal  fibres  are  seen 
passing  beyond  the  limits  of  the  dentine  into  the  enamel.  The  obHque  dark  bands  in  the 
enamel  are  the  lines  of  Retzius. 


tissue  of  the  gum,  to  the  alveolar  wall  or  to  the  cementum  of  an  adjacent  tooth, 
and  short  fibres  which  fill  in  the  interstices  between  the  long  fibres.  Many  of 
the  long  fibres  are  continued  as  calcified  fibres  into  the  cementum  on  the  one  hand 
and  into  the  bone  of  the  alveolus  on  the  other.  They  are  analogous  to  Sharpey's 
fibres  of  bone  (p.  192).  As  they  enter  the  cementum  or  bone,  the  fibres  are 
grouped  in  bundles  but  in  the  central  portion  of  the  membrane  these  bundles 
break  up  and  their  fibres  interlace  in  all  directions.  The  long  fibres  differ  in 
direction  in  different  parts  of  the  membrane.  Those  which  spring  from  the 
cementum  near  its  junction  with  enamel,  pass  out  at  right  angles  and  then  turn 
sharply  toward  the  free  margin  of  the  gum  which  they  support.  Passing  toward 
the  apex,  the  next  fibres  instead  of  bending  toward  the  free  margin  of  the  gum 
pass  out  at  right  angles  and  blend  with  the  gum  connective  tissue.     All  fibres 


THE  DIGESTIVE  SYSTE:M  235 

to  the  gums  are  more  developed  on  the  lingual  than  on  the  labial  side.  Between 
the  teeth,  fibres  of  this  level  pass  from  the  cementum  of  one  tooth  to  that  of 
the  next  adjacent,  here  also  supporting  the  free  margin  of  the  gum.  Still 
further  apically  the  fibres  are  grouped  in  coarser  bundles  to  form  the  so-called 
dental  ligament,  and  pass  over  or  into  the  edge  of  the  alveolus;  between  the  teeth 
into  the  edge  of  the  septum  oi"  into  the  cementum  of  the  adjacent  tooth.  Frcm 
ihe  dental  ligament  for  about  one-third  the  depth  of  the  root,  rather  coarse 
bundles  of  fibres  pass  from  cementum  almost  straight  to  alveolar  wall.  For 
most  of  the  remaining  two-thirds,  th^  direction  of  the  fibres  is  away  from  the 
apex,  the  bundles  tending  to  break  up  and  to  radiate  to  a  more  extended  inser- 
tion into  the  alveolar  bone.  The  apical  fibres  also  radiate  to  their  insertion  into 
bone. 

Among  the  connective-tissue  fibres  are  found  fixed  connective-tissue  cells, 
groups  or  cords  of  cells  which  are  apparently  epithelial,  and,  during  development 
and  sometimes  sparingly  later,  osteoblasts,  osteoclasts,  and  cementoblasts. 

The  fixed  connective-tissue  cells  are  described  on  p.  83. 

The  epithelioid  cells  are  mostly  arranged  in  cords  which  anastomose  to  form 
a  network.  The  cells  themselves  are  granular  and  have  oval  or  round  nuclei 
rich  in  chromatin.  In  some  places  their  arrangement  resembles  tubules,  but 
whether  they  have  a  glandular  character  is  not  known. 

Osteoblasts  and  osteoclasts  are  the  same  as  in  developing  bone  (p.  198). 
The  latter  are  present  wherever  absorption  is  taking  place.  They  are  especially 
numerous  during  the  absorption  of  the  roots  of  the  milk  teeth  to  make  way  for 
the  permanent  set. 

Cementoblasts  are  cells  which  lie  against  the  cementum  and  are  analogous 
to  the  osteoblasts,  from  which  however  they  differ  morphologically.  They  are 
flattened  and  their  protoplasm  fills  in  the  spaces  between  the  ends  of  the  fibres 
so  that  the  cell  bodies  show  the  indentations  of  the  fibres  lying  against  them. 
From  the  cementoblasts  processes  extend  into  the  cementum  in  much  the  same 
manner  as  processes  of  bone  cells  extend  into  their  canaliculi. 

Blood-vessels. — The  arteries  which  supply  the  tooth  and  peri- 
dental membrane,  enter  the  apical  portion  of  the  latter  from  the  ad- 
jacent bone  of  the  alveolus  (Fig.  134).  On  entering  the  membrane 
the  vessels  divide  into  two  main  sets  one  of  whichpasses  through  _tl}£-  -- 
foramina  of  the  apex  to  supply  the  dental  pulp,  while  the  other  passes 
along  the  outside  of  the  tooth  in  the  peridental  membrane  which  it 
supplies  (Fig.  134).  The  vessels  in  the  membrane  anastomose  with 
vessels  from  the  bone  of  the  alveolar  wall  and  at  the  margin  of  the 
alveolar  cavity  with  vessels  from  the  gums.  From  the  capillary  net- 
work veins  follow  the  arteries  back  to  the  apical  portion  of  the  mem- 
brane and  into  the  bone  at  the  bottom  of  the  alveolus.  The  arteries 
to  the  I)ulp  run  mainh'  through  its  centre  giving  off  brunches  which 
iorm  a  capilhiry  network  whi(  h  is  especially  rich  at  the  periphery  of 
the  pulp  (Fig.  138).      I-rom   these  capillaries  arise  veins  which  j)ass 


236 


THE  ORGANS 


back  through  the  apical  foramina  into  the  peridental  membrane  where 
they  unite  with  veins  from  the  membrane  and  pass  into  the  bone  of 
the  alveolus.  Enamel,  cementum,  and  dentine  are  non-vascular.  A 
marked  feature  of  the  pulp  vessels  is  the  thinness  of  their  walls,  ves- 
sels of  much  greater  calibre  than 
are  usually  classed  as  capillaries 
having  walls  of  capillary  thinness. 
Lymph  Vessels. — Most  author- 
ities have  denied  the  existence  of 
definite  lymph  channels  in  the 
pulp.  Schweitzer  on  the  other 
hand  describes  an  arborization  of 
small  lymph  vessels  in  the  pulp  of 
the  crown,  converging  to  a  few 
larger  lymph  vessels  in  the  root 
pulp  and  accompanying  the  blood- 
vessels through  the  foramina  of 
the  apex. 

Nerves. — The  distribution  of 
nerves  to  the  tooth  follows  quite 
closely  that  of  the  blood-vessels. 
Bundles  of  medullated  fibres  from 
the  bone  at  the  bottom  of  the 
alveolus  enter  the  peridental  mem- 
brane just  beneath  the  apex  where 
they  divide  into  two  main  sets, 
one  of  which  follows  the  vessels  of 
the  membrane  while  the  other 
passes  with  the  vessels  through  the 
apical  foramina  to  the  dental  pulp.  The  membrane  surrounding 
the  tooth  also  receives  nerves  from  the  bone  of  the  side  wall  of  the 
alveolus.  The  branches  to  the  pulp  pass  up  through  its  center,  giving 
off  branches  which  are  mostly  non-medullated  and  which  radiate 
toward  the  periphery  where  they  form  a  plexus  in  the  layer  of  Weil 
just  beneath  the  odontoblasts.  From  this  plexus  branches  are  given 
off  which  pass  in  between  the  odontoblasts,  some  terminating  there 
while  others  end  between  the  odontoblasts  and  the  dentine.^ 

^Noyes  calls  attention  to  the  extreme  sensitiveness  of  dentine  in  spite  of  the  fact 
that  no  nerve  fibres  have  been  demonstrated  in  its  canals,  and  believes  that  sensation 
is  carried  to  the  nerve  fibres  through  the  processes  (dentinal  fibres)  and  cell  bodies  of 
the  odontoblasts. 


Fig.  138.- 


-Diagram  of  Blood-vessels  of 
Pulp.     (Stowell). 


THE  DIGESTIVE  SYSTEM 


237 


/c■r^t•■^>°A■:V^•."■''' 


\i>jv"     "^ 


■■^V;'.'' 


Fig.  139. 


Fig.  140. 


V'"'.!'.-  '     ,  ,  .  ,  .  .'■.  .  / 


f-^^- 


Fig.  141.  Fig.  142. 

Figs.  139,  140,  141,  142.— Four  Stages  in  the  Development  of  a  Tooth  (from  lower 
jaw  of  sheep  embryo;.  (Bohm-DavidolT.)  Fig.  139,  Beginning  of  enamel  organ  show- 
ing connection  with  epithelium  of  mouth;  Fig.  140,  Later  stage  showing  same  with  first 
trace  of  papilla;  Fig.  141,  Later  stage  showing  papilla  well  formed,  the  dilTercnlialion 
of  the  enamel  i>ulp  and  of  the  inner  and  outer  enamel  cells  can  l)e  seen;  odontoblast 
appearing  along  periphery  of  the  pai)illa;  Fig.  142,  shows  also  beginning  enamel  organ  of 
permanent  tooth;  Figs.  139,  140,  Mi.Xiio,  Fig.  142, X40-  o.  Ei)ithclium  of  mouth;  h, 
its  basal  layer;  c,  suijcrficial  cells  of  enamel  organ;  d,  enamel  pulp;  />,  dental  papilla;  5, 
enamel  cells;  0,  odontoblasts;  S,  enamel  organ  of  permanent  tooth  just  beginning  to 
diflerentiate;  v,  remains  of  enamel  ledge  of  milk  tooth;  «,  surrounding  connective  tissue. 


238 


THE  ORGANS 


Development. — The  enamel  of  the  teeth  is  of  ectodermic  origin,  the  re- 
mainder of  mesodermic.  The  earliest  indication  of  tooth  formation  occurs  about 
the  seventh  week  of  intra-uterine  life  (embryos  12  to  15  mm.).  It  consists  in  a 
dipping  down  of  the  epithelium  covering  the  edge  of  the  jaw  into  the  underlying 
connective  tissue  (mesoderm)  where  it  forms  the  dental  shelf,  or  common  dental 
germ.  Soon  after  the  formation  of  the  dental  shelf,  a  groove  appears  along  the 
margin  of  the  jaw  where  the  ingrowth  of  epithelium  occurred.  This  is  known  as 
the  dental  groove.  The  epithehum  of  the  dental  shelf  is  at  first  of  uniform 
thickness.  Soon,  however,  at  intervals  along  the  outer  side  of  the  dental 
shelf,  the  cells  of  the  shelf  undergo  proliferation  and  form  thickenings,  ten  in 


h  .--- 


('i 


e     -- — :%—T- 


Fig.  143. — Developing  Tooth  from  Three-and-one-half-months'  Human  Embryo. 
X65.  (Szymonowicz.)  a,  Epithelium  of  gums;  b,  neck  of  enamel  organ;  c,  dental 
germ  of  permanent  tooth;  d,  bone  of  lower  jaw;  e,  dental  papilla;  /,  inner  enamel  cells; 
g,  enamel  pulp;  h,  outer  enam.el  cells. 


the  upper  and  ten  in  the  lower  jaw,  each  one  corresponding  to  the  position  of  a 
future  milk  tooth.  These  are  known  as  special  dental  germs,  and  remain  for 
some  time  connected  with  one  another  and  with  the  surface  epithelium  by 
means  of  the  rest  of  the  dental  ridge. 

Into  the  side  of  each  special  dental  germ  there  occurs  about  the  end  of  the 
third  month  (embryos  of  about  40  mm.)  an  invagination  of  the  underlying  con- 
nective tissue.  In  the  upper  jaw  the  invagination  takes  place  on  the  upper  and 
inner  side,  in  the  lower  jaw  on  the  lower  and  inner  side,  of  each  dental  germ. 
Each  invagination  forms  a  dental  papilla  (Fig.  141),  over  which  the  tissue  of  the 


THE  DIGESTIVE  SYSTEM 


239 


special  dental  germ  forms  a  sort  of  cap,  the  latter  being  known  from  its  sub- 
sequent function  as  the  enamel  organ,  the  papilla  itself  giving  rise  to  the  pulp 
and  dentine.  The  dental  germs  are  at  this  stage  connected  with  each  other  by 
remaining  portions  of  the  dental  shelf,  and  with  the  surface  epithelium  by 
remains  of  the  original  invagination.  The  next  step  is  the  almost  complete 
separation  of  the  special  dental  germs  and  ridge  from  the  surface  epithelium 
(Fig.  142),  and  the  formation  around  each  special  dental  germ  of  a  vacsular 
membrane,  the  dental  sac.     The  attenuated  strand  of  epithelial  cells,  which 


Epithelium  of  mouth 


Enamel  cells 


Dental  sac 


Bone  of  jaw 


Blood-vessel 


Papilla 

Fig.  144. — Longitudinal  Section  of  a  Developing  Tooth  of  a  New-born  Puppy. 
(Bonnett.)     Late  Stage. 


still  maintains  a  connection  between  the  dental  germs  and  the  epithelium  of 
the  gums,  is  known  as  the  neck  of  the  emanel  organ  and  it  is  from  this  that  an 
extension  soon  occurs  to  the  inner  side  of  the  dental  germs  of  the  milk  teeth,  to 
form  the  dental  germs  of  the  permanent  teeth  (Fig.  143,  c).  Into  the  latter, 
connective-tissue  papilla;  extend  as  in  the  case  of  the  milk  teeth.  There  are 
thus  present  as  early  as  the  fifth  month  of  foetal  existence  the  germs  of  all  milk 
and  of  some  permanent  teeth. 

The  ENAMEL  is  formed  by  the  enamel  organ.     At  the  stage  represented  in 
Fig.  145,  it  consists  of  three  layers:  (i)  The  outer  enamel  cells,  somewhat  fiat- 


240 


THE  ORGANS 


tened;  (2)  the  inner  enamel  cells,  high  columnar  epithehum;  (3)  a  layer  of  enamel 
pulp,  situated  between  the  other  layers,  and  consisting  of  stellate  anastomosing 
cells  with  considerable  intercellular  substance  (Figs.  145  and  146).  A  mem- 
brane, the  cuticular  membrane,  is  first  laid  down  between  the  inner  enamel  cells 
and  the  dentine.  Each  of  the  inner  enamel  cells  now  sends  out  a  process,  Tomes^ 
process,  from  its  inner  end.  The  processes  are  separated  by  a  considerable  amount 
of  cement,  and  are  the  beginnings  of  the  enamel  prisons.  Calcification  now  takes 
place  both  in  the  prisms  and  in  the  cement  substance,  beginning  in  the  ends  nearest 

Enamel 
Dentine    |    Enamel  prisms 


Papilla 


ItoTT*' 


Cuticle 
Basal  memb. 


of  enam.el  cells 


Fig.  145. — Section  through  Border  of  a  Developing  Tooth  of  a  New-born  Puppy. 

(Bonnett.) 


the  papilla.  As  this  proceeds  outward,  the  prisms  become  much  elongated  and 
the  cement  substance  reduced  in  amount.  Further  growth  in  thickness  of 
enamel  occurs  by  lengthening  of  the  enamel  prisms.  During  the  formation  of 
the  enamel,  the  enamel  pulp  and  the  external  enamel  cells  disappear. 

The  formation  of  enamel  in  the  milk  teeth  begins  about  the  end  of  the  fourth 
month  and  continues  until  the  eruption  of  the  teeth.  The  extent  of  the  enamel 
organ  is  considerably  greater  than  that  of  the  enamel,  the  former  covering  the 
entire  tooth,  both  root  and  crown,  with  the  exception  of  the  base  of  the  papilla 
where  the  latter  is  connected  with  the  underlying  connective  tissue.  As  the 
tooth  develops,,  the  enamel  organ  disappears  over  the  root,  remaining  to  form 
the  enamel  only  over  that  part  of  the  tooth  which  is  to  be  subsequently  exposed. 
The  function  of  the  enamel  pulp  is  not  known.  It  disappears  as  the  tooth  grows. 
It  has  been  suggested  that  it  may  furnish  nutrition  or  serve  as  an  avenue  through 
which  nutrition  reaches  the  non-vascular  enamel  organ.  It  may  serve  as  an 
area  of  least  resistance  through  which  the  tooth  grows. 


THE  DIGESTIVE  SYSTEM 


241 


a^l-a  d®  @  0  ■f^'0®®#'s 


iiSStfai^itfiVa!f.JSliii>S&Bat&:fcs*^"^^^ 


The  DENTINE  is  the  first  of  the  dental  tissues  to  become  hard.  Both  dentine 
and  pulp  develop,  as  noted  on  p.  238,  from  the  mesoderm  of  the  dental  papilla. 
When  the  latter  is  first  formed  it  is  of  the  same  structure  as  the  surrounding 
mesoderm  with  which  it  is  continuous,  except  that  it  is  somewhat  more  dense; 
later  it  assumes  more  the  character  of  embryonal  connective  tissue,  blood-vessels 
and  nerves  growing  into  it  from  the  underlying  connective  tissue.  The  most 
peripheral  cells  of  the  pulp,  those  lying  nearest  the  enamel  organ,  differentiate 
from  the  rest  of  the  pulp  to  form  a  single  layer  of  columnar  or  pyramidal  cells — 
the  odontoblasts.  The  outer  end  of  each 
cell  is  broad,  while  the  inner  end  which 
contains  the  nucleus  narrows  to  a  point 
from  which  a  dehcate  process  extends 
into  the  pulp  and  probably  anastomoses 
with  other  cell  processes.  These  cells 
are  analogous  to  the  osteoblasts  of  de- 
veloping bone  and  like  them  appear  to 
determine  the  deposition  of  lime  salts. 
The  lime  salts  are  first  laid  down  in  a 
membrane-like  structure — the  mem- 
bratia  preformativa — which  the  odonto- 
blasts apparently  form  between  them- 
selves and  the  enamel.  From  this 
membrane  the  transformation  of  the 
connective  tissue  into  dentine  progresses 
inward  toward  the  pulp,  additional 
dentine  continuing  to  be  laid  down  in 
layers,  each  new  layer  internal  to  the 
preceding.  In  this  way  the  dental 
papilla  is  reduced  in  size  to  form  the 
pulp  cavity.  In  the  outer  part  of  the 
dentine  spaces  remain  in  which  no  lime 
salts  are  deposited.  These  are  the  in- 
terglobular spaces.  As  calcification  pro- 
ceeds the  odontoblasts  do  not  become 
enclosed  within  the  dentine  as  do  the 
osteoblasts  within  bone.  They  leave  merely  long  slender  processes,  the  dental 
fibres,  lying  in  minute  channels  through  the  dentine,  dental  canals,  while  the 
bodies  of  the  cells  form  a  single  layer  along  the  inner  margin  of  the  dentine. 
There  are  thus  no  lacunae  and  no  cells  within  the  dentine.  This  relation  of 
odontoblasts  to  dentine,  and  probably  the  original  odontoblasts,  persist,  not 
only   throughout  embryonic  but  through  adult  life. 

While  the  tooth  lies  within  the  gum,  the  somewhat  condensed  connective 
tissue  which  surrounds  it  constitutes  the  dental  sac. 

As  the  germs  of  the  milk  teeth  develop,  the  dental  shelf  broadens  by  extend- 
ing inward  toward  the  tongue.  Ahmg  this  inner  margin  appear  the  germs  of 
the  permanent  teeth,  the  development  of  the  various  teeth  structures  from  the 
germs  being  identical  with  the  process  described  in  the  case  of  the  milk  teeth, 

16 


Fig.  146. — From  Cross-section  through 
a  Developing  Tooth.  X  720.  (Bohm  and 
von  Davidoff.)  Note  close  relationship 
between  odontoblasts  and  tissue  of  dental 
pulp,  a,  Dental  pulp;  b,  odontoblasts;  c, 
dentine;  d,  inner  enamel  cells;  e,  enamel 
pulp. 


242  THE  ORGANS 

Twenty  of  the  permanent  teeth  correspond  in  position  to  the  twenty  milk 
teeth,  whUe  twelve  new  molar  germs,  six  in  the  upper  and  six  in  the  lower  jaw, 
represent  the  true  molars  of  the  adult.  The  first  permanent  tooth  germ  to  appear 
is  that  of  the  first  molar,  about  the  beginning  of  the  fifth  month  (embryos  of 
about  i8o  mm.).  It  lies  just  behind  the  second  molar  of  the  milk  dentition. 
The  germs  of  the  incisors  and  canines  appear  about  the  end  of  the  sixth  month, 
those  of  the  premolars,  which  replace  the  milk  molars,  in  the  beginning  of  the 
eighth  month.  The  germs  of  the  second  and  third  (wisdom  teeth)  molars  do 
not  appear  until  after  birth,  those-  of  the  former  at  about  six  months,  of  the 
latter  during  the  fifth  year. 

The  CEMENTUM  is  developed  by  ossification  of  that  part  of  the  dental  sac 
which  covers  the  root,  its  development  being  similar  to  subperiosteal  bone 
formation  (p.  201),  without  the  formation  of  Haversian  systems. 

TECHNIC 

(i)  Teeth  are  extremely  difficult  organs  from  which  to  obtain  satisfactory 
material  for  study.  Sections  of  hard  (undecalcified)  and  of  decalcified  teeth 
may  be  prepared  in  the  same  manner  as  sections  of  bone— technics  i,  p.  196;  2, 
p.  197.  The  decalcified  tooth  should  include  if  possible  the  alveolar  margin  of  the 
jaw,  so  that  in  longitudinal  sections  the  mode  of  implantation  and  the  relation 
of  the  tooth  to  the  surrounding  structures  can  be  seen. 

(2)  For  the  study  of  developing  teeth,  embryo  pigs,  sheep,  cats,  dogs,  etc.,  are 
suitable.  For  the  early  stages  foetal  pigs  should  be  five  to  six  inches  long;  for  the 
intermediate,  ten  to  twelve  inches.  The  later  stages  are  best  obtained  from  a 
small  new-born  animal,  e.g.,  kitten  or  small  pup.  The  jaw — preferably  the 
lower — or  pieces  of  the  jaw  are  fixed  in  formalin-Miiller's  fluid  (technic  5,  p.  7), 
hardened  in  alcohol,  and  decalcified  (page  10).  Subsequent  treatment  is  the 
same  as  for  developing  bone  (technic  i,  p.  203). 

The  Pharynx 

The  wall  of  the  pharynx  consists  of  three  coats — mucous,  muscu- 
lar, and  fibrous. 

I.  The  mucous  membrane  has  a  surface  epithelium  and  an  un- 
derlying stroma. 

The  EPITHELIUM  is  stratified  squamous  except  in  the  region  of  the 
posterior  nares,  where  it  is  stratified  columnar  ciKated,  continuous 
with  the  similar  epithelium  of  the  nasal  mucosa. 

The  STROMA,  or  tunica  propria,  consists  of  mixed  fibrous  and 
elastic  tissue  infiltrated  with  lymphoid  cells.  In  certain  regions 
these  cells  form  distinct  lymph  nodules  (see  pharyngeal  tonsils,  page 
180).  Beneath  the  stratified  squamous  epithelium  the  stroma  is 
thrown  up  into  numerous  low  papillae.     These  are  absent  in  regions 


THE  DIGESTIVE  SYSTE:M  243 

covered  by  ciliated  cells.  Bounding  the  stroma  externally  is  a 
strongly  developed  layer  of  longitudinal  elastic  fibres,  the  elastic 
limiting  layer,  which  separates  the  stroma  from  the  muscular  coat 
and  sends  stout  bands  in  between  the  muscle  bundles  of  the  latter. 

2.  The  muscular  coat  hes  beneath  the  elastic  layer  and  is 
formed  of  very  irregularly  arranged  muscle  fibres  belonging  to  the 
constrictor  muscles  of  the  pharynx. 

3.  The  fibrous  coat  consists  of  a  dense  network  of  mixed  fibrous 
and  elastic  tissue.  It  has  no  distinct  external  Hmit,  and  binds  the 
pharynx  to  the  surrounding  structures. 

The  distribution  of  blood-vessels,  lymphatics,  and  nerves  is 
similar  to  that  in  the  oral  mucosa. 

Small,  branched,  tubular,  mucous  glands  are  present  in  the  stroma, 
and  extend  down  into  the  intermuscular  connective  tissue.  They 
are  most  numerous  near  the  opening  of  the  Eustachian  tube. 

TECHNIC 

For  the  study  of  the  structure  of  the  walls  of  the  pharynx,  material  should 
be  prepared  as  in  technic  2,  p.  223. 

n.  THE  FOREGUT 
The  CEsophagus 

The  walls  of  the  oesophagus  are  continuous  with  those  of  the  phar- 
ynx and  closely  resemble  the  latter  in  structure.  They  consist  of 
four  layers,  which  from  within  outward  are  mucous,  submucous, 
muscular,  and  fibrous  (Fig.  147J. 

1 .  The  mucous  membrane  resembles  that  of  the  pharynx  except 
that  beneath  the  stroma  is  a  well-developed  nmscularis  mucosce  com- 
posed of  smooth  muscle  cells  arranged  longitudinally.  The  muscu- 
laris  mucosae  forms  a  complete  coat  only  in  the  lower  part  of  the 
cesophagus.  The  epithelium  is  stratified  squamous  and  rests  upon 
a  papillatcd  stroma. 

2.  The  submucosa  is  composed  of  loosely  arranged  fibrous  and 
elastic  tissue.  It  contains  mucous  glands,  the  larger  blood-vessels, 
lymj>hati(s,  aiul  ncr\'cs. 

3.  The  Muscular  Coat.  In  the  uj>j)cr  \H>rl.'um  of  the  (X'soj)hagus 
this  coat  is  composed  of  striated  muscle  fibres;  in  the  middle  j)orti()n, 
of  mixed  striated  and  smooth  muscle.     In  the  lower  j)ortion  there  are 


244 


THE  ORGANS 


two  distinct  layers  of  smooth  muscle,  an  inner  circular  and  an  outer 
longitudinal.     The  latter  is  not  continuous. 

4.  The  fibrous  coat  consists  of  bundles  of  white  fibrous  tissue  with 
many  elastic  fibres.  It  serves  to  connect  the  oesophagus  with  the 
surrounding  structures. 

Two  kinds  of  glands  occur  in  the  oesophagus. 


Fig.  147. — Transverse  Section  through  Wall  of  Dog's  (Esophagus.  X18.  (Bohra 
and  von  Davidoff.)  a,  EpitheHum;  b,  stroma;  c,  muscularis  mucosse;  d,  submucosa;  e, 
circular  muscle  layer;  /,  longitudinal  muscle  layer;  g,  fibrous  layer. 


(i)  Mucous  Glands. — These  are  of  the  same  structure  as  those 
of  the  tongue,  but  much  smaller.  They  he  in  the  submucosa  and  are 
distributed  throughout  the  entire  oesophagus,  though  most  numerous 
in  its  upper  third.  The  ducts  pass  obUquely  downward  on  their  way 
to  the  surface.  Just  before  entering  the  muscularis  mucosse  the  duct 
widens  out  to  form  a  sort  of  ampulla.  Beyond  this  it  again  becomes 
narrow  and  enters  the  epithelium  in  the  depression  between  two 
adjacent  papillee.  A  small  lymph  nodule  is  usually  attached  to  the 
duct  as  it  passes  through  the  tunica  propria. 

(2)  Simple  Branched  Tubular  Glands. — These  resemble  the 
glands  of  the  cardiac  end  of  the  stomach,  but  branch  much  more 


THE  DIGESTIVE  SYSTE:M  245 

profusely.  Some  contain  both  chief  and  acid  cells,  others  only  chief 
cells  (see  stomach,  page  249) .  They  He  in  the  tunica  propria,  and  are 
for  the  most  part  confined  to  a  narrow  zone  at  the  lower  end  of  the 
oesophagus  and  to  the  level  of  the  fifth  tracheal  ring.  Scattered 
groups  also  occur  in  other  regions. 

The  distribution  of  blood-vessels,  lymphatics,  and  nerves  in  the 
oesophagus  is  similar  to  their  distribution  in  the  mouth  (p.  222).  Be- 
tween the  two  muscular  coats  the  nerve  fibres  form  plexuses  in  which 
are  many  sympathetic  nerve  cells.  These  plexuses  are  analogous  to 
the  plexuses  of  ^Sleissner  in  the  stomach  and  intestine. 

TECHNIC 

Remove  a  portion  of  the  wall  of  the  oesophagus,  wash  carefully  in  normal 
salt  solution,  and  pin  out,  mucous-membrane  side  up,  on  a  piece  of  cork.  Fix  in 
formalin-Miiller's  fluid  and  harden  in  alcohol  (technic  5,  p.  7).  Transverse  or 
longitudinal  sections  should  be  cut  through  the  entire  thickness  of  the  wall.  If 
the  details  of  the  muscular  coat  are  to  be  studied,  sections  from  at  least  three 
different  levels  should  be  taken:  one  near  the  upper  end,  one  at  about  the 
middle,  and  the  other  in  the  lower  third.  Stain  with  haematoxylin-eosin  or 
hjematoxyhn-picro-acid-fuchsin  (technic  i,  p.  20;  3,  p.  21)  and  mount  in  balsam. 

General  Structure  of  the  Walls  of  the  Gastro-intestinal 

Canal 

The  walls  of  the  stomach  and  intestines  are  made  up  of  four  coats 
(Fig.  148) .  These  from  the  lumen  outward  are  mucous,  submucous, 
muscular,  and  serous. 

I.  The  mucous  membrane  (Fig.  148)  consists  of  surface  epithe- 
lium, glands,  stroma,  and  muscularis  mucosae.  The  surface  epithe- 
lium is  simple  columnar  and  rests  upon  a  distinct  basement  membrane. 
The  arrangement  of  the  glands  and  the  nature  of  the  gland  cells  differ 
in  different  parts  of  the  tract.  The  stroma  is  a  loosely  arranged, 
richly  cellular  connective  tissue,  which  in  many  places  is  so  infiltrated 
with  lymphoid  cells  as  to  constitute  diffuse  lymphatic  tissue.  In 
other  places  it  contains  circumscribed  masses  of  lymphatic  tissue, 
lymph  nodules.  The  amount  of  stroma  depends  upon  the  closeness 
with  which  the  glands  are  packed.  The  muscularis  mucosa  consists 
of  smooth  muscle  cells,  which  have  a  generally  longitudinal  arrange- 
ment. Where,  however,  the  muscularis  mucosae  is  thick  there  are 
usually  two  distinct  layers — an  inner  circular  and  an  outer  longitudi- 


246 


THE  ORGANS 


nal.  Folds  of  considerable  extent  occur  in  the  mucous  membrane. 
Those  of  the  stomach  are  known  as  rugm,  and  are  not  constant, 
depending  upon  the  degree  of  distention  of  the  organ.  Those  of  the 
small  intestine  are  much  more  definite,  and  are  known  as  valvules 
conniventes. 


Fig.  148, — Diagram  of  Structure  of  Wall  of  Gastro-intestinal  Canal.  A,  Mucous 
membrane;  a,  glands;  b,  epithelium;  c,  goblet  cells;  d,  stroma;  e,  inner  circular;/,  outer 
longitudinal  layers  of  g,  muscularis  mucosae.  B,  Submucosa.  C,  Muscular  coat;  h,  its 
inner  circular  layer;  j,  its  outer  longitudinal  layer;  i,  intermuscular  connective- tissue 
septum.     D,  serous  coat;  k,  its  connective-tissue  layer;  /,  its  endothelial  layer. 


2.  The  submucosa  (Fig.  148)  is  a  loose  connective-tissue  stucture. 
It  contains  the  larger  blood-vessels,  lymphatics,  and  nerves. 

3.  The  muscular  coat  (Fig.  148)  consists  of  two  layers  of  smooth 
muscle,  which  in  the  intestine  are  sharply  differentiated  into  an  inner 
circular  and  an  outer  longitudinal.  In  the  stomach  the  direction  of 
the  layers  of  the  muscular  coat  is  less  definite.     A  narrow  layer  of 


THE  DIGESTIVE  SYSTEM 


247 


connective  tissue  separates  the  two  layers  of  muscle.     From  this, 
septa  extend  into  the  muscle  tissue,  separating  it  into  bundles. 

4.  The  serous  coat  (Fig.  148)  is  the  visceral  layer  of  the  perito- 
neum. It  consists  of  a  thin  layer  of  connective  tissue  covered  by  a 
single  layer  of  mesothelium.  Along  the  attachment  of  the  mesentery 
the  serous  coat  is  wanting. 


\, 


J) 


cd 


Fig.  149. — Section  through  Junction  of  Oisophagus  and  Stomach  of  Man.  X121. 
(Schafer.)  Oe,  (Esophagus;  M,  stomach;  cd,  cardiac  glands;  wd,  dilated  ducts  of  cardiac 
glands;  S,  stroma;  E,  stratified  squamous  epithelium  of  oesophagus;  mm,  muscularis 
mucosae;  cd,  irregularly  cut  tubules  of  cardiac  glands;  dd,  cardiac  glands  in  lower  end  of 
the  oesophagus;  ii,  limit  of  stratified  oesophageal  epithelium. 

The  subdivisions  of  the  gastro-intestinal  canal  dilTcr  from  one 
another  mainly  in  regard  to  the  structure  of  their  mucous  membranes, 
and  especially  in  regard  to  the  structure  of  the  glands  of  the  niucous 
membrane  and  submucosa. 


The  Stomach 

At  the  junction  of  oesophagus  and  stomach   there  is  an  abrupt 
transition  from  the  stratified  squamous  epil helium  of  the  former  with 


248 


THE  ORGANS 


its  smooth  surface  to  the  simple  columnar  epithelium  of  the  latter 
with  its  elevations  and  depressions.  In  the  deeper  structures  the  line 
of  demarcation  is  not  so  abrupt,  the  muscularis  mucosae  of  the  oesoph- 
agus being  continuous  with  that  of  the  stomach,  and  glands  of  the 
stomach  type  extending  up  under  the  stratified  epitheUum'  of  the 
oesophagus  (Fig.  149). 

I .  The  mucous  membrane  of  the  stomach  is  folded  into  ridges  or 
rugcs,  the  height  and  number  of  which  depend,  as  already  noted,  upon 


Fig.  1 50. — Outline  Diagram  of  Stomach  to  showLocation  of  Different  Kinds  of  Glands- 

c,  Cardia;  p,  pylorus;  vvvvvv,  cardiac  glands;  ,  fundus  glands;  +  +  +  ++,  pyloric 

glands;  000000,  intestinal  type  glands  (of  Lieberkuhn).     (Jouvenal.) 

the  degree  of  distention  of  the  organ.  The  rugae  are  most  prominent 
in  the  collapsed  organ,  almost  absent  when  the  organ  is  fully  dis- 
tended. In  addition  to  the  rugae  the  entire  mucous  membrane  is 
studded  with  minute  depressions  barely  visible  to  the  naked  eye,  the 
so-called  gastric  pits  (Fig.  152,  Mg).  These  mark  the  openings  of  the 
gastric  glands.  In  the  fundus  they  are  comparatively  shallow,  ex- 
tending through  about  one-fifth  the  thickness  of  the  mucosa;  in  the 
pylorus  the  pits  are  much  deeper,  extending  through  half  or  more  of 
the  thickness  of  the  mucous  membrane  (compare  Figs.  152  and  156). 
The  Epithelium. — This  is  of  the  simple  columnar  type,  covers  the 
entire  surface  of  the  gastric  mucosa  and  extends  down  into  the  pits 
(Fig.  152).  The  cells  are  of  the  high,  clear,  mucous  type  (Fig.  153, 
M  and  M').     The  end  of  the  cell  toward  the  lumen  is  clear,  usually 


THE  DIGESTIVE  SYSTE.M  249 

consists  mostly  of  mucus,  and  consequently  stains  lightly.  There 
is  no  such  distinct  cuticle  as  in  the  intestine.  The  basal  end  of  the 
cell  contains  the  spheroidal,  oval,  or  sometimes  flattened  nucleus,  is 
granular,  and  takes  a  darker  stain.  The  amount  of  mucus  in  the  cell 
depends  upon  its  functional  condition.  The  cells  rest  upon  a  distinct 
basement  membrane. 

The  Gastric  Glands.— Extending  from  the  bottoms  of  the  pits, 
their  epithelium  continuous  with  that  of  the  pits  themselves,  are  the 
gastric  glands.     These  are  of  two  main  kinds,  fundus  or  peptic  glands, 


Gastric  ^^^B::^lBHBhiB^  jS^HHESH^^^^^^B       Gastric  pits 


Fig.  151. — Surface  View  of  Mucous  Membrane  of  Stomach  showing  gastric  pits 

(Spalteholz). 

distributed  through  the  greater  part  of  the  gastric  mucosa,  and  py- 
loric glands,  confined  to  the  immediate  region  of  the  pylorus. 

The  fundus  glands  (Fig.  152)  are  simple,  sometimes  branched, 
tubular  glands,  of  which  from  three  to  seven  open  into  each  gastric 
pit.  They  extend  through  the  entire  thickness  of  the  stroma,  to  the 
muscularis  mucosae. 

Each  gland  consists  of  (i)  a  mouth  opening  into  the  pit;  (2)  a 
constricted  portion,  the  neck;  (3)  the  body  or  main  portion  of  the 
tubule;  and  (4)  a  slightly  dilated  and  bent  blind  extremity,  the 
fundus  (Fig.  152).  The  mouth  marks  the  transition  from  the  higher 
epithelium  of  the  pit  to  the  low  cuboidal  of  the  neck  (Fig.  153,  h). 
In  the  body  and  fundus  of  the  gland  two  types  of  cells  are  found: 
(a)  chief  cells  (central,  peptic,  or  adelomorphous),  and  {b)  parietal 
cells  facid,  oxyntic,  or  delomorphous). 

The  chief  cells  (Figs.  153,  154)  are  the  more  numerous.  They  are 
of  the  low  columnar  type,  often  pyramidal  with  apices  directed  toward 
the  lumen.     Their  bases  rest  either  on  the  basement  membrane  or 


250 


THE  ORGANS 


against  the  parietal  cells.  The  appearance  which  these  cells  present 
depends  upon  their  functional  condition  (p.  272).  They  usually 
appear  clear  and  granular  and  take  a  light  stain. 

The  parietal  cells  (Fig.  153,)  are  oval  or  polygonal  in  shape,  and 

.  lie  here  and  there  against  the  base- 
ment membrane.  The  nucleus  is 
spherical,  somewhat  larger  than  that 
of  the  chief  cell,  and  is  usually  situ- 
ated at  the  center  of  the  cell.  There 
may  be  two  nuclei.  The  protoplasm 
is  finely  granular  and  in  the  fresh 
unstained  condition  appears  clearer 
than  that  of  the  chief  cells.  The 
parietal  cells  stain  intensely  with  the 
aniline  dyes  with  the  result  that  in 


Fig.  152.  Fig.  153. 

Fjg  152.— Vertical  Section  through  the  Mucous  Membrane  of  the  Fundus  of  the 
Stomach.  X8s.  (KoUiker.)  Mg,  Gastric  pits;  h,  neck;  k,  body;  g,  fundus  of  peptic 
glands;  h,  chief  cells;  h,  parietal  cells;  w,  muscularis  mucosa. 

Fig.  153.— Cross-sections  at  Various  Levels  of  Peptic  Glands  of  Stomach.  X400. 
(KoUiker.)  M,  Section  through  gastric  pit  near  surface;  M  ,  section  through  gastric 
pit  near  bottom;  h,  mouth  of  gland;  k,  neck;  g,  body  near  fundus;  a,  chief  ceUs;  b, 
parietal  cells,    j 

stained  "specimens  the  two  kinds  of  "cells  are  in  marked  contrast,  the 
parietal  cells  being  much  darker  than  the  chief  cells.  Although  lying 
against  the  basement  membrane  and  frequently  pushing  it  out  so  as 


THE  DIGESTIVE  SYSTEM 


251 


to  form  little  protuberances  beyond  the  even  line  of  the  gland  tubule, 
the  parietal  cells  always  maintain  a  connection  with  the  lumen. 
This  is  accomplished  by  means  of  little  clefts  between  the  chief  cells, 
intercellular  secretory  tubules,  which  extend  down  to  the  parietal  cells. 
By  means  of  the  method  of  Golgi  may  be  demonstrated  not  only  the 
intercellular  secretory  tubules,  but  also  the  fact  that  upon  reaching  the 
cells  these  are  continuous  with  a  network  of  minute  spaces  within  the 
cell — the  intracellular  secretory  tubules  (Figs.  154  and  155).     Parietal 


Fig.  154. — Sections  through  Different  Parts  of  a  Fundus  Gland  of  Human  Stomach. 

A,  mouth  of  gland;  cells  resemble  surface  cells  except  that  they  are  shorter. 

B,  neck  of  gland;  cp,  principal  cells;  cpm,  mucous  cells;  ch,  parietal  cells,  one  contain- 
ing two  nuclei. 

C,  middle  portion  of  gland;  cp,  chief  cells;  ch,  parietal  cells. 

Z?,  deeper  part  of  gland;  cp,  chief  cells  containing  secretory  granules,  and  at  their 
bases  ergastoplasm  filaments  itrg):  at  c  are  shown  intracellular  secretory  canals  i)cne- 
trating  base  of  cell;  ch,  parietal  cells,  one  of  which  shows  canaliculus  leading  to  lumen  of 
gland  (\),  the  latter  being  cut  twice  in  section  owing  to  its  irregular  course. 

/s,  blind  end  of  gland;  cp,  chief  cells  with  secretion  granules  and  ergastoplasm  fila- 
ments (erg);  ch,  parietal  cells,  one  containing  three  nuclei;  cpm,  mucous  cells;  /,  lumen  of 
gland.     X2S0.     (Prenant.) 


cells  are  not  distributed  uniformly  throughout  the  gland,  but  are 
most  numerous  in  the  body,  where  they  frequently  almost  obscure 
the  chief  cells.  In  the  fundus  of  the  gland  parietal  cells  are  less  nu- 
merous. For  this  reason  and  because  of  the  wider  lumen  of  the  fundus, 
transverse  and  longitudinal  sections  of  this  part  of  the  tubule  are 
most  satisfactory  for  the  study  of  the  relations  of  the  two  kinds  of 
cells  (Figs,  152  and  153).     Mitosis  is  most  active  at  the  junction  of 


252 


THE  ORGANS 


the  neck  and  body  of  the  tubule  which  has  consequently  been  desig- 
nated the  "growing  point"  of  the  tubule. 

Lying  near  the  basement  membrane  among  the  bases  of  the  colum- 
nar epithelial  cells  are  small  spherical  or  irregular  cells  with  dark 
nuclei.  These  are  young  epithelial  cells  which  from  their  function 
are  known  as  "replacing  cells"  (see  page  73). 

The  PYLORIC  GLANDS  (Figs.  156  and  157)  are  simple  branched 
tubular  glands,  several  of  which  open  into  each  of  the  deep  pyloric  pits. 

The  glands,  though  short,  are  quite 
tortuous,  so  that  in  sections  the  tubules 
are  seen  cut  mainly  transversely  or 
obliquely.  In  most  of  the  pyloric  glands 
but  one  type  of  cell  is  found.  These 
resemble  the  chief  cells  of  the  fundus, 
but  present  a  more  uniform  appear- 
ance, probably  due  to  the  absence  of 
parietal  cells.  As  in  the  fundus,  "re- 
placing cells"  Ue  between  the  bases  of 
the  columnar  epitheUal  cells.  Parietal 
cells  are  not  always  entirely  absent,  but 
occur  here  and  there  in  the  pyloric 
tubules,  especially  near  the  fundus. 

The  transition  from  fundus  to 
pylorus  is  not  abrupt,  but  is  marked  by 
a  "transitional  border  zone,"  in  which 
fundus  and  pyloric  glands  are  inter- 
mingled, and  in  which  are  also  found  single  glands  which  resemble 
in  structure  both  cardiac  and  pyloric. 

In  the  transition  zone  between  oesophagus  and  stomach  are  found 
glands  which  resemble  those  found  in  the  lower  end  of  the  oesophagus 
(p.  244).  Their  cells  are  clear  resembling  those  of  the  pyloric  glands. 
Some  of  the  tubules  have  parietal  cells.  They  have  been  designated 
cardiac  glands  and  pass  over  by  gradual  transition  into  the  fundus 
glands.  There  are  also  found  in  the  stomach  glands  which  are  appar- 
ently identical  in  structure  with  those  of  the  intestine  (p.  260) .  Most 
of  these  resemble  the  glands  of  Lieberkiihn  and  are  distributed  in 
small  groups  mainly  in  the  pylorus  and  lesser  curvature.  Glands 
resembling  Brunner's  glands  have  also  been  described. 

The  STROMA  (Figs.  152  and  156) -or  tunica  propria,  in  which  the 
glands  are  embedded,  consists  of  mixed  fibrillar  and  reticular  connective 


Fig.  155. — ^Longitudinal  Section 
of  Fundus  of  Gland  from  Pyloric 
End  of  Dog's  Stomach.  (Golgi 
method.  See  5,  p.  29.)  a,  Lumen 
of  gland;  h,  intracellular  canals  in 
parietal  cells;  c,  cut-off  portion  of 
parietal  cell;  d,  chief  cells;  e,  inter- 
cellular canals  leading  from  lumen 
of_^gland  to  canals  in  parietal  cells. 


THE  DIGESTIVE  SYSTE:\I 


253 


tissue  infiltrated  with  lymphoid  cells.  In  the  fundus  of  the  stomach 
the  glands  are  so  closely  packed  that  the  stroma  is  reduced  to  thin 
strands,  which  pass  up  between  the  glands  and  also  separate  them 
from  the  muscularis  mucosae.  In  the  pylorus  the  glands  are  more 
widely  separated  and  the  stroma  is  correspondingly  greater  in  amount. 
In  both  fundus  and  pylorus  thicker  strands  of  stroma  surround  a  num- 


My 


mm 


iySr^c^A^^-^^*^ 


mm 


mj^^ 


W^ 


f 


Fig.  156.  Fig.  157. 

Fig.  1 56.— Vertical  Section  through  Mucous  Membrane  of  Pyloric  End  of  Stomach. 
X85.  (Kolliker.)  Mg,  Gastric  pit;  b,  blood-vessel  in  stroma;  d,  longitudinal  section 
of  body  of  gland;  m,  muscularis  mucosae. 

Fig.  157. — Pyloric  Gland  from  Vertical  Section  through  Wall  of  Dog's  Stomach. 
(Ebstein.j  m,  Gastric  pit  in  which  are  seen  some  transversely  cut  cells;  n,  neck  of  gland; 
/,  fundus  cut  transversely. 

her  of  ghmd  tubules,  thus  separating  them  into  more  or  less  well- 
defined  groups.  In  addition  to  the  diffuse  lymphatic  tissue  of  the 
stroma,  closely  packed  aggregations  of  lymphoid  cells  are  found  in  the 
shaj)e  of  distinct  nodules,  known  as  "solitary  follicles."  These  occur 
throughout  the  entire  gastric  mucosa,  but  are  most  numerous 
in  the  pylorus.     The  nodules  are  usually  egg-shaped,  their  apices 


254  THE  ORGANS 

lying  just  beneath  the  epithelium,  their  bases  resting  upon  the  muscu- 
laris  mucosae.  Less  commonly  they  lie  partly  in  the  submucosa. 
Over  the  nodules  the  epithelium  is  more  or  less  infiltrated  with  migra- 
tory leucocytes.  Most  of  the  nodules  contain  germinal  centres 
around  which  the  lymphoid  cells  are  more  closely  packed  than  else- 
where (see  page  169). 

The  MUSCULARis  MUCOSA  (Figs.  152  and  156,  m)  may  consist  of 
a  single  layer  of  smooth  muscle  with  cells  arranged  longitudinally  or 
obliquely,  or  there  may  be  two  distinct  layers,  an  inner  circular  and 
an  outer  longitudinal.  From  the  muscularis  mucosae  single  cells 
and  groups  of  cells  extend  into  the  stroma  between  the  gland  tubules. 

2.  The  submucosa  consists  of  connective  tissue,  loosely  arranged, 
many  elastic  fibres,  and  some  fat.  It  contains  the  larger  blood- 
vessels and  nerves,  including  the  plexus  of  Meissner  (p.  271). 

3.  The  muscular  coat  is  usually  described  as  consisting  of  three 
layers,  an  inner  oblique,  a  middle  circular,  and  an  outer  longitudinal. 

In  the  fundus  the  muscle  bundles  run  in  various  directions,  so  that 
the  division  of  the  muscular  coat  into  layers  having  definite  directions 
.can  be  made  out  only  in  the  pylorus.  Here  the  inner  and  middle 
layers  are  thickened  to  form  the  sphincter  pylori.  In  the  connective 
tissue  which  separates  the  groups  of  muscle  cells  are  collections 
of  sympathetic  nerve  cells  and  fibres,  which  while  much  less  distinct, 
are  analogous  to  Auerbach's  plexus  of  the  intestine. 

4.  The  serous  coat  consists  of  a  layer  of  loosely  arranged  connec- 
tive tissue  covered  by  a  single  layer  of  mesothelium. 

TECHNIC 

(i)  Remove  a  human  stomach  (not  more  than  two  or  three  hours  after  death) 
or  that  of  a  recently  killed  dog.  Open  along  the  lesser  curvature,  and  carefully 
remove  the  excess  of  mucus  by  washing  with  normal  saline.  Cut  pieces  through 
the  entire  thickness  of  the  wall,  one  from  the  fundus  and  one  from  the  pylorus; 
pin  out,  mucous  membrane  side  up,  on  pieces  of  cork,  fix  in  formalin-Miiller's 
fluid  (technic  5,  p.  7)  or  in  Zenker's  fluid  (technic  9,  p.  8),  and  harden  in  alcohol. 
Sections  are  cut  as  thin  as  possible,  care  being  taken  that  the  plane  is  such  that 
the  glands  are  cut  longitudinally,  stained  with  hsematoxylin-eosin  (technic  i,  p. 
20),  and  mounted  in  balsam. 

(2)  Instead  of  removing  pieces  of  stomach  and  pinning  them  out  on  cork,  as 
suggested  in  the  preceding  technic,  the  entire  stomach  may  be  filled  with  the 
fixative,  the  ends  being  tied,  and  then  placed  in  a  large  quantity  of  the  fixing 
fluid.  After  fixation,  pieces  are  removed  and  hardened  in  graded  alcohols.  If 
this  method  is  used,  great  care  must  be  taken  not  to  overdistend  the  organ,  only 


THE  DIGESTIVE  SYSTEM  255 

very  moderate  distention  being  desirable.     Further  treatment  is  the  same  as  in 
the  preceding  technic  (i). 

(3)  For  comparison  of  resting  with  active  gastric  cells,  preparations  should  be 
made  from  the  stomach  of  an  animal  that  has  been  for  from  twenty-four  to  forty- 
eight  hours  without  food,  and  from  a  stomach  during  active  digestion.  Fix  in 
Zenker's  fluid  as  in  technic  (i),  above.  Examine  unstained  sections  and  sections 
stained  with  ha?matoxylin-eosin. 

(4)  Sections  through  the  junction  of  oesophagus  and  stomach  and  through  the 
junction  of  stomach  and  duodenum  furnish  instructive  pictures.  They  should 
be  prepared  as  in  technic  (i). 

(5)  For  the  study  of  the  distribution  of  the  blood-vessels  sections  of  an 
injected  stomach  should  be  made.  This  is  best  accomplished  by  selecting  a 
small  animal,  such  as  a  rat  or  guinea-pig,  and  injecting  in  toto  through  the  as- 
cending aorta,  or  by  injecting  only  the  hind  part  of  the  animal  through  the  ab- 
dominal aorta.     Technic,  p.  25. 


III.  THE  MIDGUT 

The  Small  Intestine 

On  passing  from  stomach  to  small  intestine  the  rugae  of  the  former 
disappear,  but  are  replaced  by  much  more  definite  foldings  of  the 
mucosa,  the  valvulcB  conniventes  (Fig.  159).  These  folds  involve  the 
entire  thickness  of  the  mucous  membrane  and  part  of  the  submucosa. 
They  are  in  general  parallel  to  one  another,  and  pass  in  a  circular  or 
obUque  manner,  partly  around  the  lumen  of  the  gut.  The  entire 
surface  of  the  intestine,  including  the  valvula),  is  studded  with  minute 
projections  just  visible  to  the  naked  eye,  and  known  as  villi  (Figs.  160 
and  161).  These  involve  only  the  epithelium  and  stroma,  although 
they  also  contain  some  muscular  elements  derived  from  the  muscularis 
mucosae.  The  viUi  differ  in  shape  in  the  different  parts  of  the  small 
intestine,  being  leaf-shaped  in  the  duodenum,  rounded  in  the  jejunum, 
club-shaped  in  the  ileum.  The  valvulai  conniventes  and  the  viUi  are 
characteristic  of  the  small  intestine.  It  is  important  to  note  that 
while  the  pits  of  the  stomach  are  depressions  in  the  inucous  membrane, 
the  intestinal  vilh*  are  definite  projections  above  its  general  surface 
(Fig.  158). 

The  wall  of  the  intestine  consists  of  the  same  four  coats  described 
as  constituting  the  wall  of  the  stomach,  mucosa,  submucosa,  muscu- 
laris, anrl  serosa. 

1.  The  mucosa,  a.-,  in  the  stomach,  is  com])ose<l  of  a  lining  epilhe- 
lium,  stroma,  glands,  and  muscularis  mucosa.    Of  these,  the  epithelium, 


256 


THE  ORGANS 


the  stroma,  and  cells  from  the  muscularis  mucosae,  are  concerned  in 
the  formation  of  the  vilK. 

The  VILLUS  consists  of  a  central  core — a  fold  of  the  stroma — of 
mixed  fibrous  and  reticular  tissue  infiltrated  with  lymphoid  cells,  and 
of  a  covering  epithelium. 

The  epithelium  is  disposed  in  a  single  layer,  separated  from  the 
underlying  connective  tissue  by  a  basement  membrane.  It  consists  of 
two  apparently  quite  different  kinds  of  cells,  columnar  cells  Sindgoblet  or 
mucous  cells.     The  former  are  the  more  num.erous  and  are  peculiar 


Fig.  158. — Section  through  Junction  of  Pylorus  and  Duodenum.  (Klein.)  V,  Villi 
of  duodenum;  d,  stomach,  showing  gastric  pits;  b,  apex  of  a  solitary  lymph  nodule;  c, 
crypt  of  Lieberkiihn;  s,  secreting  tubules  of  Brunner's  glands;  g,  pyloric  glands;  t, 
tubules  of  Brunner's  glands  in  submucosa  of  stomach;  ;w,  muscularis  mucosae. 


to  the  intestine,  while  the  mucous  cells  are  identical  with  those  found 
in  other  mucous  membranes.  The  columnar  cells  are  quite  elastic 
and  while  generally  long  and  narrow,  vary  as  to  length  and  breadth 
as  they  adapt  themselves  to  movements  of  the  intestine.  The 
peculiarity  of  these  cells  is  a  striated  free  border,  their  contiguous 
free  borders  uniting  to  form  the  so-called  cuticular  membrane  (Fig. 
163,  c).  By  means  of  special  technic  these  striations  can  be  resolved 
into  delicate  parallel  lying  rods  or  fibrils.  They  have  been  interpreted 
by  some  as  marking  channels  through  the  cuticle,  by  others  as  a 
fibrillar  arrangement  of  the  protoplasm.     In  some  forms  tiny  swell- 


THE  DIGESTIVE  SYSTE:M 


257 


ings  at  the  proximal  ends  of  the  fibrils,  resembhng  the  basal  granules 
of  ciliated  cells  (p.  76)  have  led  to  the  suggestion  that  the  fibrils  are 
alHed  to  ciHa.  The  nuclei  of  these  cells  are  ovoid  and  usuall}'  lie  near 
the  middle  or  in  the  base  of  the  cell.  Scattered  among  the  columnar 
cells  are  the  mucous  or  goblet  cells  (Figs.  162  and  163,  h).  These 
vary  in  appearance  according  to  the  amount  of  secretion  which  they 
contain.  A  cell  at  the  beginning  of  secretion  contains  onlyta  small 
amount  of  mucus  near  its  free  border.     As  secretion  increases  the 


Fig.  159. — Vertical  Longitudinal  Section  of  Human  Jejunum  (X16)  (Stohr) /includ- 
ing two  valvulae  conniventes.  a,  Villi,  in  many  of  which  the  stroma  has  shrunken  away 
from  the  epithelium  leaving  a  clear  space,  X  X.  Lying  free  in  the  lumen  of  the  gut  are 
seen  sections  of  villi  cut  in  various  directions,  b,  Epithelium;  c,  stroma;  d,  crypts  of 
Lieberkiihn;  X,  solitary  lymi)h  nodule  with  germinal  centre;  e,  tissue  of  submucosa 
forming  centre  of  one  of  the  v^alvulae  conniventes;/,  submucosa;  g,  inner  circular  layer 
of  musc\e;Ji,  outer  longitudinal  layer  of  muscle;  i,  Auerbach's  plexus;/,  serous  coat. 

mucus  gradually  replaces  the  cytoplasm  until  the  latter  is  represented 
only  by  a  crescentic  mass  containing  a  flattened  nucleus  and  pressed 
against  the  basement  membrane.  The  cell  now  discharges  its  mucus 
upon  the  free  surface.  The  goblet  cells  possess  no  thickened  Ijorder, 
appearing,  when  seen  from  the  surface,  as  openings  surrounded  on 
all  sides  by  the  cuticula;  of  the  adjacent  columnar  cells.  Opinions 
differ  as  to  the  relation  of  the  mucous  to  the  cokimnar  cell.  Some 
authorities  consider  them  two  different  and  independent  cells.     The 

17 


258 


THE  ORGANS 


majority,  however,  look  upon  the  mucous  cell  as  specialization  of  the 
columnar  cell.  Again  opinions  differ  as  to  whether  the  mucous  cell, 
having  discharged  its  secretion,  dies  or  re-secretes,  or  returns  to  the 


Mouths  of  crypts 


Lympli  nodules 


Villi 


Fig.  i6o. — Surface  View  of  Small  Intestine  near  upper  end,  showing  viUi  and  one  solitary- 
lymph  nodule.     Xi2.     (Spalteholz.) 


/   "- 


Fig.  i6i. — Vertical  Section  through  Mucous  Membrane  of  Human  Jejunum.  X8o. 
(Stohr.)  a  and  b,  Artifacts  due  to  shrinkage;  c,  intestinal  crypts  (Lieberkiihn) ;  d, 
obique  and  transverse  sections  of  crypts;  e,  stroma;/,  epithelium;  g,  tangentially  cut 
villi;  k,  muscularis  mucosae;  ^,submucosa. 


THE  DIGESTIVE  SYSTEM 


259 


condition  of  the  columnar  cell.  Small  spherical  cells  with  deeply 
staining  nuclei  are  found  in  varying  numbers  among  and  sometimes 
udthin  the  epithelial  cells. ^  These  are  so-called  wandering  cells, 
migratory  leucocytes,  from  the  underlying  stroma  (Figs.  162,  h,  and 
163,  /).  Other  cells  \vith  dark-staining  nuclei,  "replacing  cells,"  are 
found  between  the  bases  of  the  columnar  cells  (pages  73  and  252), 


Fig.  162. 


Fig.  163. 


Fig.  162. — Longitudinal  Section  of  Villus  from  Small  Intestine  of  Dog.  (Piersol.) 
a,  Columnar  epithelium;  b,  goblet  cells;  h,  leucocytes;  c,  basement  membrane;  d,  core  of 
villus;  e,  blood-vessels;/,  lacteal. 

Fig.  163. — Cross-section  of  a  Villus  of  Human  Small  Intestine.  X.';30-  (Kolliker.) 
The  stroma  of  the  villus  has  shrunken  away  from  the  epithelium,  b,  Goblet  cell;  c, 
cuticula  showing  striations;  e,  columnar  epithelial  cell;  gm,  basement  membrane  with 
nuclei;  /,  leucocyte  in  epithelium;  I',  leucocyte  just  beneath  epithelium:  tn  large  leuco- 
cyte in  stroma;  ch,  central  chyle  vessel;  g,  blood-vessel. 

In  addition  to  the  connective-tissue  and  lymphoid  cells,  which 
constitute  the  main  bulk  of  the  villus  core  (Figs.  162  and  163),  iso- 
lated smooth  muscle  cells  derived  from  the  muscularis  mucosa)  occur, 
running  in  the  long  axis  of  the  villus.  A  single  lymph  or  chyle  vessel 
(Fig.  162,  /;  163,  ch)  with  distinct  endothehal  walls  traverses  the 
centre  of  each  villus,  ending  at  its  tip  in  a  slightly  dilated  blind 
extremity.     As  it  is  usually  seen  collapsed,  it  appears  as  two  closely 

'  iJavidofT  considers  these  cells  leucocytes  in  |)roccss  of  formation.  IFc  describes 
some  of  the  columnar  cells  as  having  two  nuclei,  one  of  which  remains  within  the  cell, 
while  the  other  is  extruded  with  a  little  cytoplasm  as  a  leucocyte. 


260 


THE  ORGANS 


appro?dmated  rows  of  flat  cells  with  bulging  nuclei.  The  capillaries 
of  the  villus  lie  for  the  most  part  away  from  the  chyle  vessel,  just 
beneath  the  basement  membrane  (Fig.  162,  e;  163,  g). 

From  the  depths  of  the  depressions  between  the  villi,  simple 
tubular  glands— glands  or  crypts  of  Lieberkiihn  (Figs.  161  and 
164) — extend  down  through  the  stroma  as  far  as  the  muscularis 
mucosEe.     These  crypts  are  Uned  with  an  epitheHum  similar  to  and 

continuous  with  that  covering  the  villi. 
The  cells  are,  however,  lower,  and  there 
are  fewer  goblet  cells.  In  addition  to 
these  cells  there  are  also  found  in  the 
depths  of  the  crypts  of  Lieberkiihn 
peculiar  coarsely  granular  cells,  the  cells 
of  Paneth  (Fig.  164,  k).  They  are 
found  in  man  and  in  rodents,  but  do 
not  occur  in  the  carnivora.  They 
probably  produce  a  specific  secretion, 
the  nature  of  which  is  unknown.  In 
contrast  with  the  stomach,  where  most 
active  mitosis  is  at  the  junction  of  the 
neck  and  body  of  the  gland  (page  251), 
the  most  active  cell  proliferation  in  the 
intestinal  epitheUum  is  at  the  bottoms 
of  the  crypts. 

Fig.  i64.-LongituSiial  Section  The    Stroma,    besides    forming    the 

of  Fundus  of  Crypt  of  Lieberkiihn.  centres  of  the  villi,  fills  in  the  spaces 
XS30.     (Kolliker.)     6,  Goblet  ceU  ^       c  t  u     ^  --u  A 

showing  mitosis;  e,  epithelial  cell;    between  the  crypts  of  Lieberkuhn  and 

k,  cell  of  Paneth;  I,  leucocyte  in  between  the  latter  and  the  muscularis 
epitheJium;  m,  mitosis  m  epitheuai 

cell.     Surrounding   the  crypt  is    mucosae.     In  places  the  lymphoid  cells 

seen   the   stroma   of  the  mucous  ,       .  i     j     -        r  j*  i*      j. 

membrane.  3,re    closely    packed   to    lorm    distinct 

nodules  or  "solitary  folHcles,"  such  as 

are  found  in  the  stomach  (see  page  253). 

Peyer's  Patches  (agminated   follicles)   (Fig.  165). — These  are 

groups  of  lymph  nodules  found  mainly  in  the  ileum,  especially  near 

its  junction  with  the  jejunum.     They  always  occur  on  the  side  of 

the  gut  opposite  the  attachment  of  the  mesentery.     Each  patch 

consists  of  from  ten  to  seventy  nodules,  so  arranged  that  the  entire 

patch  has  a  generally  oval  shape,  its  long  diameter  lying  lengthwise 

of  the  intestine.     The  nodules  of  which  a  patch  is  composed  lie  side 

by  side.     Their  apices  are  directed  toward  the  lumen  and  project 


THE  DIGESTIVE  SYSTEM 


261 


Fig.  165.— Transverse  Section  of  Cat's  Small  Intestine  through  a  Pcyer's  Patch. 
(Stohr.)  a.  Villi;  b,  crypts;  c,  longitudinal  muscle  layer;  d,  circular  muscle  layer;  e, 
lymph  nodules;/,  muscularis  mucosa;;  g,  submucosa. 


Solitary 
lymph  nodules 


Pc-ycr's  patch 


r 


Fig.  160.     .^uriacc  View  of  Mucous  Memhrant-  of  Small  Intestine  (Ileum),  .'•liowing 
Peyer's  patch  (Spallcholz). 


262 


THE  ORGANS 


almost  through  the  mucosa,  being  uncovered  by  villi,  a  single  layer 
of  columnar  epithelium  alone  separating  their  surfaces  from  the 
lumen  of  the  gut.  The  bases  of  the  nodules  are  not  confined  to  the 
stroma,  but  usually  spread  out  in  the  submucosa.  The  relation  of 
the  patch  to  the  stroma  and  submucosa  can  be  best  appreciated  by 
following  the  course  of  the  muscularis  mucosae.     This  is  seen  to  stop 

abruptly  at  the  circumference 
of  the  patch,  appearing  through- 
out the  patch  as  isolated  groups 
of  smooth  m.uscle  cells.  The 
nodules  rarely  remain  distinct, 
but  are  confluent  with  the  ex- 
ception of  their  apices  and 
bases.  It  should  be  noted  that 
both  solitary  nodules  and 
Peyer's  patches  are  structures 
of  the  mucosa,  and  that  their 
presence  in  the  submucosa  is 
secondary. 

The  muscularis  mucosa 
(Figs.  i6i  and  167)  consists  of 
an  inner  circular  and  an  outer 
longitudinal  layer  of  smooth 
muscle. 

2.  The  submucosa  (Figs, 
159,  161.  167)  consists,  as  in  the 
stomach,  of  loosely  arranged 
connective  tissue  and  contains 
the  larger  blood-vessels.  It  is 
free  from  glands  except  in  the 
duodenum,  where  it  contains  the  glands  of  Brunner  (Fig.  167). 
These  are  branched  tubular  glands  lined  with  a  granular  columnar 
epithelium  similar  to  that  of  the  pyloric  glands.  The  ducts  are  also 
lined  with  simple  columnar  epithelium.  They  pass  through  the 
muscularis  mucosas  and  empty  either  into  a  crypt  of  Lieberkiihn  or 
on  the  surface  between  the  villi.  Brunner's  glands  frequently  occur 
in  the  pylorus,  and  it  is  not  uncommon  for  the  pyloric  glands  to 
extend  downward  somewhat  into  the  duodenum.  Meissner's  plexus 
of  nerve  fibers,  mingled  with  groups  of  sympathetic  ganglion  cells, 
lies  in  the  sub-mucosa  (see  page  271). 


'"'  ■ '"''"t^'.'u. 

_  Fig.  167. — From  Vertical  Longitudinal  Sec- 
tion of  Cat's  Duodenum  to  show  Brunner's 
Glands.  (Larrabee.)  a,  Villus;  h,  epithe- 
lium; c,  stroma;  d,  glands;  e,  muscularis 
mucosEe;  /,  Brunner's  glands;  g,  submucosa; 
h,  circular  muscle  layer. 


THE  DIGESTIVE  SYSTEM  263 

3.  The  muscular  coat  (Figs.  159  and  167)  consists  of  two  well- 
defined  layers  of  smooth  muscle,  an  inner  circular  and  an  outer 
longitudinal.  Connective-tissue  septa  divide  the  muscle  cells  into 
groups  or  bundles,  while  between  the  two  layers  of  muscle  is  a  con- 
nective-tissue septum  which  varies  greatly  in  thickness  at  different 
places  and  contains  a  plexus  of  nerve  fibres  and  sympathetic  ganglion 
cells  known  as  the  plexus  of  Auerbach  (see  page  270). 

4.  The  serous  coat  consists  as  in  the  stomach  of  loose  connective 
tissue  covered  by  a  single  layer  of  mesothelium. 

IV.  THE  ENDGUT 

The  Large  Intestine 

The  wall  of  the  large  intestine  consists  of  the  same  four  coats 
which  have  been  described  as  constituting  the  walls  of  the  stomach 
.and  small  intestine,  mucous,  submucous,  muscular,  and  serous. 

I.  The  mucous  membrane  has  a  comparatively  smooth  surface, 
there  being  neither  pits  as  in  the  stomach  nor  villi  as  in  the  small 
intestine  (Fig.  168).  The  glands  are  of  the  simple  tubular  variety, 
are  considerably  longer  than  those  of  the  small  intestine,  are  almost 
straight,  and  extend  through  the  entire  thickness  of  the  stroma. 
Owing  to  the  closeness  with  which  the  gland  tubules  are  packed,  the 
amount  of  stroma  is  usually  small.  The  surface  cells  (Fig.  168,  a) 
are  very  high  and  narrow,  with  small,  deeply  placed  nuclei,  and  are 
not  usually  intermingled  with  goblet  cells.  Passing  from  the  surface 
down  into  the  glands,  the  cells  become  somewhat  lower  and  goblet 
ceUs  become  numerous  (Fig.  169,  a  and  d).  Both  superficial  and 
deep  cells  rest  upon  a  basement  membrane  similar  to  that  in  the  small 
intestine.  The  stroma  also,  though  less  in  amount,  is  similar  in  struc- 
ture to  the  stroma  of  the  small  intestine. 

The  MUSCULARis  MUCOSA  (Fig.  169,  c)  consists  of  an  inner  circular 
and  an  outer  longitudinal  layer  of  smooth  muscle. 

2.  The  submucosa  (Fig.  168,  e)  consists  of  loosely  arranged  con- 
nective tissue.  It  contains  large  blood-vessels  and  the  nerve  plexus 
of  Meissner  (see  page  271).  Solitary  lymph  follicles  occur  throughout 
the  mucous  membrane  of  the  large  intestine.  While  properly  con- 
sidered as  structures  of  the  stroma  from  which  they  originate,  the 
follicles  lie  mainly  in  the  submucosa.  (For  details  of  structure  see 
page  169.) 


264 


THE  ORGANS 


3.  Of  the  musciilaris  (Fig.  168)  the  inner  circular  layer  only  is 
complete,  the  muscle  tissue  of  the  external  longitudinal  coat  being 
arranged  mainly  as  three  strong,  fiat,  longitudinal  bands,  the  lineae 
coli.  Between  these  bands  the  longitudinal  muscular  coat  is  either 
very  thin  or  entirely  absent.     In  the  connective  tissue,  lying  to  the 


■:^:-, b 


d 


g- 


Fig.  168.  Fig.  169. 

Fig.  168. — From  Vertical  Longitudinal  Section  of  Cat's  Large  Intestine.  (Larra- 
bee.)  a,  Epithelium;  b,  stroma;  c,  fundus  of  gland;  d,  muscularis  mucosae;  e,  submucosa;f, 
circular  muscle  layer;  g,  longitudinal  muscle  layer;  h,  serous  coat;  i,  Auerbach's  plexus. 

Fig.  169. — From  Vertical  Longitudinal  Section  of  the  Mucous  Membrane  of  the 
Human  Large  Intestine.  (Technic  i,  p.  275.)  a,  Mucous  (goblet)  cells;  h,  fundus  of  a 
gland  cut  obliquely;  c,  muscularis  mucosae;  d,  lumen  of  a  gland  cut  longitudinally;  e, 
stroma  between  the  glands;/,  leucocytes  in  the  epithelium;  g,  stroma  between  fundi 
of  glands  and  muscularis  mucosae. 

outer  side  of  the  circular  muscle  coat,  is  the  nerve  plexus  of  Auerbach. 
(For  details  see  page  270.) 

4.  The  serous  coat  consists,  as  in  the  stomach  and  small  intestine, 
of  loose  connective  tissue  covered  by  a  single  layer  of  mesothelium. 


THE  DIGESTIVE  SYSTEM 


265 


The  Vermiform  Appendix 

The  vermiform  appendix  is  a  diverticulum  from  the  large  intes- 
tine. Its  walls  are  continuous  with  those  of  the  latter,  and  closely 
resemble  them  in  general  structure.  There  are  the  same  four  coats, 
mucous,  submucous,  muscular,  and  serous. 


^.ob< 


ot'O  u  ft 


\\ 


^^. 


t''' 
; 


%. 


^:Si.v, 


Fig.  170. — Transverse  Section  of  Human  Vermiform  Appendix.  (Technic  2,  p.  275.) 
a,  Mesoappendix;  A,  serous  membrane  (serosa);  c,  outer  longitudinal  muscle  layer;  d, 
inner  circular  muscle  layer;  e,  submucosa;  /,  groups  of  fat  cells  in  submucosa;  g,  blood- 
vessels in  submucosa;  h,  lymph  nodules;  i,  stroma;  j,  glands  opening  into  lumen  and  cut 
ia  various  planes;  muscularis  mucosae  not  present. 


I.  The  mucous  membrane  (Fig.  170)  consists  of  epithelium, 
glands,  str(;ma,  and  muscuhiris  mucosic.  The  epiUielium  resembles 
that  of  the  large  intestine.  The  glands  vary  in  number,  but  are  usu- 
ally much  less  closely  packed  than  in  the  large  intestine.  They  are 
most  numerous  in  the  ai)pendices  of  infants  and  children.  The 
gland  luhides  (Fig.  170,7)  are  usually  rudimentary,  but  in  most  cases 
have  the  same  structure  as  the  intestinal  glands,  and  are  evidently 


266  THE  ORGANS 

functional  as  they  contain  mucous  cells  in  all  stages  of  secretion.  In 
consequence  of  the  wider  separation  of  the  tubules  the  stroma  is  more 
abundant  than  in  the  large  intestine,  but  has  the  same  structure. 
The  muscularis  mucosa  is  usually  fairly  distinct  as  a  thin  circularly 
disposed  band  of  smooth  muscle  cells  just  beneath  the  stroma.  It  is 
not  always  present.  In  some  cases  the  mucosa  as  such  is  practically 
absent,  being  replaced  by  fibrous  tissue.  This  condition  is  especially 
common  after  middle  age,  and  may  or  may  not  be  associated  with 
obliteration  of  the  lumen. 

2.  The  submucosa  (Fig.  170,  e)  is  similar  to  that  of  the  intestine. 

3.  The  muscular  coat  varies  greatly,  both  as  to  thickness  and 
as  to  the  amount  of  admixture  of  fibrous  tissue.  The  inner  circular 
layer  (Fig.  170,  d)  is  usually  thick  and  well  developed.  The  outer 
longitudinal  layer  (Fig.  170,  c)  differs  from  that  of  the  large  intestine 
in  having  no  arrangement  into  lineae,  the  muscle  tissue  forming  a  con- 
tinuous layer.  Less  commonly  a  more  or  less  marked  tendency  to  an 
arrangement  of  the  cells  of  the  longitudinal  coat  into  bundles,  be- 
tween which  the  outer  coat  is  thin  or  wanting,  is  observed. 

4.  The  serosa  has  the  usual  structure  of  peritoneum. 

The  lymph  nodules  (Fig.  170,  h)  constitute  the  most  conspicuous 
feature  of  the  appendix.  They  lie  mainly  in  the  submucosa.  In 
children  and  young  adults  the  nodules  are  oval  or  spherical;  in  later 
life  somewhat  flattened.  The  nodules  may  be  entirely  distinct,  or 
may  be  arranged  as  in  a  Peyer's  patch  with  distinct  apices  and  bases, 
but  with  their  central  portions  confluent.  The  muscularis  mucosae 
either  passes  through  the  superficial  portions  of  the  nodules,  or,  where 
they  are  separated  from  the  lumen,  passes  over  them. 

The  distribution  of  blood-vessels,  lymphatics,  and  nerves  is 
similar  to  that  in  the  large  intestine. 

The  Rectimi 

I.  The  mucous  membrane  of  the  rectum  has  a  structure  similar 
to  that  of  the  large  intestine.  The  glands  are  longer  and  the  mucosa 
is  consequently  somewhat  thicker.  In  the  lower  part  of  the  rectum 
definite  longitudinal  foldings  of  the  mucosa  occur,  the  so-called 
columncB  rectales.  A  change  in  the  character  of  the  mucous  membrane 
begins  at  the  upper  end  of  the  columnae  rectales.  Here  the  simple 
columnar  epithelium  of  the  gut  passes  over  into  a  stratified  squamous 
epithehum,  beneath  which  is  a  papillated  stroma.     The  glands  con- 


THE  DIGESTIVE  SYSTEM 


267 


tinue  for  a  short  distance  beyond  the  change  in  the  epithelium, 
but  soon  completely  disappear.  At  the  anus  there  is  a  transition 
from  mucous  membrane  to  skin  similar  to  that  described  as  occurring 
at  the  margin  of  the  lips  (page  220). 

2.  The  submucosa  is  similar  in  structure  to  that  of  the  large 
intestine. 

The  muscularis  of  the  rectum  differs  from  that  of  the  large  intes- 
tine in  that  the  longitudinal  layer  is  continuous  and  thick. 


Fig.  171. — Mucous  Membrane  of  Human  Rectum,  a,  Superficial  epithelium,  com- 
posed almost  wholly  of  mucous  cells,  the  columnar  cells  lying  between  them  being  so 
compressed  as  to  appear  as  thin  dark  lines;  gl,  lumen  of  gland  of  Lieberkuhn.  X60. 
CPrenant.) 

The  serous  coat  is  absent  in  the  lower  part  of  the  rectum,  being 
replaced  by  a  fibrous  connective-tissue  layer,  which  connects  the  rec- 
tum with  the  surrounding  structures. 


The  Peritoneum,  Mesentery,  and  Omentum 

The  peritoneum  (see  also  p.  165)  is  a  serous  membrane  which  lines 
the  walls  of  the  abdomen  (parietal  peritoneum)  and  is  reflected  over 
the  contained  viscera  (visceral  i)erit<)neum).  It  consists  of  two 
layers,  a  connective-tissue  stroma  and  inrsol helium.  'J'he  stroma 
consists  of  loosely  arranged   connective-tissue  bundles,  which  inter- 


268  THE  ORGANS 

lace  in  a  plane  parallel  to  the  surface.  There  are  numerous  elastic 
fibres,  especially  in  the  deeper  layer  of  the  parietal  peritoneum. 
There  are  comparatively  few  connective- tissue  cells.  The  mesothe- 
lium  consists  of  a  single  layer  of  fiat  polygonal  cells  with  bulging 
nuclei.  The  cells  have  irregular  wavy  outlines,  which  are  easily  dem- 
onstrated with  silver  nitrate  (Fig.  26).  The  shape  of  the  cells  varies 
considerably  according  to  the  direction  in  which  the  tissues  are 
stretched.  Over  some  parts,  e.g.,  the  liver  and  intestine,  the 
peritoneum  or  serosa  is  thin  and  very  closely  attached.  In  places 
where  the  peritoneum  is  freely  movable,  a  considerable  amount  of 
loose  connective  tissue,  rich  in  elastic  fibres  and  containing  varying 
numbers  of  fat  cells,  connects  the  peritoneum  with  "the  underlying 
tissue.  This  is  known  as  the  '^subserous  tissue.'"  The  peritoneum  is 
well  supplied  with  blood-vessels  and  lymphatics.  The  former  give 
rise  to  a  rich  capillary  network. 

The  mesentery  is  a  sheet  of  loosely  arranged  connective  tissue 
covered  with  peritoneum.  It  is  reflected  from  the  post-abdominal 
wall  to  the  viscera,  and  serves  to  carry  to  these  organs  their  blood- 
vessels, lymphatics,  and  nerves.  In  the  case  of  the  stomach,  duo- 
denum, and  large  intestine,  the  mesentery  is  comparatively  short, 
and  the  organs  are  therefore  quite  firmly  fixed  to  the  abdominal  wall. 
In  the  case  of  the  small  intestine  the  mesentery  is  long  and  the  intes- 
tine, therefore,  freely  movable.  The  mesentery  is  richly  supplied 
with  lymph  nodes  and  there  is  usually  a  considerable  amount  of  fat. 
From  the  mesentery,  the  peritoneum  passes  over  to  and  envelops  the 
viscera. 

The  omentum  (Fig.  26)  is  a  sheet  of  tissue  which  passes  from  the 
liver  to  the  lesser  curvature  of  the  stomach  (gastro-hepatic  omentum) 
to  which  it  is  attached,  and  from  the  greater  curvature  of  the  stomach 
to  the  transverse  colon  (greater  omentum) .  It  is  similar  in  structure 
to  the  mesentery,  and  contains  usually  much  fat  and  many  lymph 
nodes.  Its  connective-tissue  bundles  are  arranged  in  networks,  the 
strands  and  meshes  of  which  vary  greatly  in  size  and  shape.  The 
strands  are  covered  by  a  single  layer  of  mesothelium. 

Blood-vessels  of  the  Stomach  and  Intestines 

The  arteries  reach  the  gastro-intestinal  canal  through  the  mesen- 
tery and  pass  through  the  muscular  coats  to  the  submucosa,  where 
they  form  an  extensive  plexus  of  large  vessels   (Heller's  plexus) 


THE  DIGESTIVE  SYSTEM 


269 


(Fig.  172,  c).  Within  the  muscular  coats  the  main  arteries  give  off 
small  branches  to  the  muscle  tissue.  From  the  plexus  of  the  submu- 
cosa  two  main  sets  of  vessels  arise,  one  passing  outward  to  supply  the 
muscular  coats,  the  other  inward  to  supply  the  mucous  membrane 
(Fig.  172).  Of  the  former  the  larger  vessels  pass  directly  to  the  inter- 
muscular septum,  where  they  form  a  plexus  from  which  branches  are 
given  off  to  the  two  muscular  tunics.     A  few  small  branches  from  the 


.■/  B  c 

Fig.  172. — Scheme  of  Blood-vessels  and  Lymphalics  of  Stomach.  Xyo-  (Szy- 
monowicz,  after  Mall.)  a,  jNIucous  membrane;  h,  muscularis  mucosa;;  c,  submucosa;  d, 
inner  circular  muscle  layer;  e,  outer  longitudinal  muscle  layer;  A,  blood-vessels;  B, 
structure  of  coats;  C,  lymphatics. 

larger  recurrent  vessels  also  supply  the  inner  muscular  layer.  Of  the 
branches  of  the  submucosa  plexus  which  pass  to  the  mucous  mem- 
brane, the  shorter  supply  the  muscularis  mucosa,',  while  the  longer 
branches  pierce  the  latter  to  form  a  capillary  plexus  among  the  glands 
of  the  stroma.  From  the  capillaries  small  veins  take  origin  wliich 
pierce  the  muscularis  mucosa?  and  form  a  close-mcshcd  venous  plexus 
in  the  submucosa  (Fig.  172).  These  \r\,  turn  give  rise  to  larger  veins, 
which  accompany  the  arteries  into  the  mesentery. 

In  the  small  intestine  the  distribution  of  the  blood-vessels  is 
modified  by  the  presence  of  the  viUi  (Fig.  174).  Each  villus  receives 
one  small  artery,  or,  in  the  case  of  the  larger  villi,  two  or  three  small 


270 


THE  ORGANS 


arteries.  The  artery  passes  through  the  long  axis  of  the  villus  close 
under  the  epithehum  to  its  summit,  giving  off  a  network  of  fine  capil- 
laries, which  for  the  most  part  He  just  beneath  the  epithelium. 

From  these,  one  or  two  small  veins  arise 
which  lie  on  the  opposite  side  of  the 
villus  from  the  artery. 

Lymphatics  of  the  Stomach  and 
Intestine 


Small  lymph  or  chyle  capillaries 
begin  as  blind  canals  in  the  stroma  of 
the  mucous  membrane  among  the  tubular 
glands  (Fig.  172).  In  the  small  intestine 
a  lymph  (chyle)  capillary  occupies  the 
centre  of  the  long  axis  of  each  villus, 
ending  in  a  bHnd  extremity  beneath  the 
epithehum  of  its  summit  (Fig.  174). 
These  vessels  unite  to  form  a  narrow- 
meshed  plexus  of  lymph  capillaries  in  the 
deeper  part  of  the  stroma,  lying  parallel 
to  the  muscularis  mucosae.  Vessels  from 
this  plexus  pass  through  the  muscularis 
mucosae  and  form  a  wider  meshed  plexus 
of  larger  lymph  vessels  in  the  submucosa. 
A  third  lymphatic  plexus  Hes  in  the  con- 


FiG.  173. — Diagram  of  wall 
of  Stomach  to  show  General  Dis- 
position of  Lymphatics  a,  Term- 
inal lymph  channel  in  tissues 
separating  glands;  b,  superficial 
lymphatic  plexus  in  connective 
tissue  surrounding  bases  of 
glands;  c,  submucous  lymphatic 
plexus;  d,  intermuscular  lym- 
phatic plexus;  e,  subperitoneal 
lymphatic  plexus.     (Cuneo.) 


nective  tissue  which  separates  the  two 
layers  of  muscle.  From  the  plexus  in  the  submucosa,  branches  pass 
through  the  inner  muscular  layer,  receive  vessels  from  the  intermus- 
cular plexus,  and  then  pierce  the  outer  muscular  layer  to  pass  into 
the  mesentery  in  company  with  the  arteries  and  veins. 


Nerves  of  the  Stomach  and  Intestines 

The  nerves  which  supply  the  stomach  and  intestines  are  mainly 
non-medullated  sympathetic  fibres.  They  reach  the  intestinal  walls 
through  the  mesentery.  In  the  connective  tissue  between  the  two 
layers  of  muscle,  these  fibres  are  associated  with  groups  of  sym- 
pathetic ganglion  cells  to  form  the  plexus  myentericus  or  plexus  of 
Auerhach.    The  dendrites  of  the  ganghon  cells  interlace,  forming  a 


THE  DIGESTIVE  SYSTEil 


271 


large  part  of  the  plexus.  The  axones  are  grouped  together  in  small 
bundles  of  non-medullated  fibres,  which  pass  into  the  muscular  coats, 
where  they  form  intricate  plexuses,  from  which  are  given  off  club- 
shaped  terminals  to  the  smooth  muscle  cells.  From  Auerbach's 
plexus  fibres  pass  to  the  submucosa,  where  they  form  a  similar  but 


Fig.  174. — Scheme  of  Blood-vessels  and  Lymphalics  of  Human  Small'JnLestine. 
(From  Bohm  and  von  Davidoff,  after  Mall.)  a,  Central  lacteal  of  villus;  b,  lacteal;  c, 
stroma;  d,  muscularis  mucosa;;  e,  submucosa;/,  plexus  of  lymph  vessels;  g,  circular  mus- 
cle layer;  /!,^plexus  of  lymph  vessels;  i,  longitudinal  muscle  layer;  y,  serous  coat;  k,  vein; 
/,  artery;  m,  base  of  villus;  n,  crypt;  0,  artery  of  villus;  p,  vein  of  villus;  q,  epithelium. 

finer-meshed,  more  delicate  plexus,  also  associated  with  groups  of 
sympathetic  ganglion  cells,  the  plexus  of  Meissner.  Both  fibres  and 
cells  are  smaller  than  those  of  Auerbach's  plexus.  From  Meissner's 
plexus  delicate  fibrils  pass  to  their  terminations  in  submucosa,  mus- 
cularis mucosaj,  and  mucous  membrane. 


Secretion  and  Absorption 

The  secretory  activities  of  ('jjilhelial  cells  have  alreafly  been  men- 
tioned (page  212).  The  ei)ithelium  of  the  gastro-intestinal  tract 
must  be  considered  as  having  two  main  functions:  (i)  The  secretion 


272  THE  ORGANS 

of  substances  necessary  to  digestion;  and  (2)  the  absorption  of  the 
products  of  digestion. 

(i)  Secretion. — The  production  of  mucus  takes  place  in  the 
mucous   or  goblet  cell,   which  is  present  throughout  the  gastro- 
enteric mucosa  and,  as  already  mentioned,  probably  represents  a 
differentiation  of  the  ordinary  columnar  epithelial  cell.     The  chief 
_    _ — .  -.  cells,  "peptic  cells,"  of  the 

stomach  glands  are  compar- 
atively clear  during  fasting, 
with  development  of  ergas- 
toplasm  in  their  basal  ends. 
With  the  onset  of  digestion 
these  cells  increase  in  size 
and  become  generally  cloudy 
from  development  of  gran- 
ules with  reduction  of  the 
ergastoplasm.  These  gran- 
ules represent  a  pre-ferment 

Frc.  i75.-Section  through  Glands  of  Fundus  ^^     pepsinogen  and      with 
of    Human   btomach   in   Condition  of    Hunger.             .           . 

Xsoo.     (Bohm  and  von  Davidoff.)     a,  Stroma;  their      discharge  into      the 

b,  parietal  cell;   c,  lumen;  d,  chief  cell.  ,  ,  , ,         ^  ^    ^^  n 

lumen  of  the  gland,  the  cells 
again  become  smaller,  clearer,  and  assume  the  resting  condition. 
Bensley  and  Theohara  have  recently  very  clearly  demonstrated  the 
secretory  chain  in  the  chief  cells  from  ergastoplasm  or  basal  filaments 
through  pepsinogen  granules  to  pepsin.  While  some  authorities 
still  contend  that  a  minor  pepsin-forming  role  is  played  by  the 
pyloric  glands,  the  above  facts  together  with  the  fact  that  activity 
of  the  chief  cells  (Fig.  176)  is  coincident  with  an  increase  in  the  pepsin 
found  in  the  stomach,  and  that  the  amount  of  pepsinogen  in  the  gastric 
mucosa  is  proportionate  to  the  number  of  granules  in  the  chief  cells, 
(Langley  and  Sewell)  may  be  accepted  as  proving  these  cells  the  main 
if  not  the  sole  producers  of  pepsin,  and  the  granules  as  some  stage 
in  the  elaboration  of  the  ferment.  As  their  name  of  "acid  cells" 
would  indicate,  the  parietal  cells  have  been  considered  the  source 
of  the  hydrochloric  acid  of  the  stomach.  While  doubt  still  exists 
as  to  the  function  of  these  cells,  recent  investigations  make  it  probable 
that  they  secrete  substances  which  as  chlorides  are  transformed  into 
hydrochloric  acid  by  the  action  of  the  carbonic  acid  of  the  blood. 
According  to  some  authorities  other  cells  assist  in  the  production 
of  the  stomach  acid.     The  cells  of  Brunner's  glands  undergo  changes 


THE  DIGESTIVE  SYSTE:M  273 

during  digestion,  which  are  somewhat  similar  to  those  described  as 
occurring  in  the  chief  cells  of  the  stomach  glands.  By  some  they  are 
believed  to  be  concerned  in  the  production  of  pepsin,  by  others  to 
play  a  special  role  in  the  secretion  of  one  or  more  of  the  intestinal 
ferments.  The  only  function  of  the  surface  epithehum  and  of  that 
of  the  intestinal  crypts  which  has  yet  been  determined  is  the  secretion 
of  mucus.  The  cells  of  Paneth  are  typical  gland  cells  containing 
secretion  granules  and  probably  produce  a  specific  secretion.  (See 
also  page  260.)     Whether  this  secretion  is  the  so-called  "inverse 


V'--; 


& 


& 


i&.^«  -'-'l-'  *V,-i.' 


Fig.  1 76. — Section  through  Glands  of  Fundus  of  Human  Stomach  during  Diges- 
tion. Xsoo.  (Bohm  and  von  Davidoff.)  a,  Lumen;  b,  stroma;  c,  chief  cell;  d, 
parietal  cell. 

ferment"  or  ''invertifi"  which  changes  cane  sugar  into  glucose  and 
levulose  or  one  of  the  other  intestinal  ferments  has  not  been  deter- 
mined. It  has  been  known  that  pancreatic  fluid  is  inactive  toward 
albuminoids  unless  mixed  with  intestinal  secretions.  This  is  due 
according  to  Pavlow  to  a  special  ferment  " enterokinase."  According 
to  some  this  is  a  secretion  of  the  epithelium,  to  others  it  is  elaborated 
by  eosinophile  leucocytes  which  pass  through  the  intestinal  wall, 
and  become  a  part  of  the  intestinal  secretion. 

(2)  Aii.soRPTiON  OF  F^AT. — While  various  other  products  of  diges- 
tion are  absorbed  by  the  intestine,  the  absorption  of  fat  is  the  one 
most  easily  observed  and  the  one  of  most  interest  from  the  histological 
standpoint  because  the  passage  of  the  droplets  can  be  seen  under  the 
microscope.     After  feeding  fat,  fatty  acids,  or  soaps,  fat  globules  are 

18 


274  THE  ORGANS 

found  to  have  penetrated  the  intestinal  mucosa,  and  may  be  seen  in 
(a)  the  epithehal  cells,  (b)  the  leucocytes,  and  (c)  the  lacteals  of  the 
villi  (Fig.Jiyy).  Fat  globules  are  never  seen  in  the  thickened  free 
borders  of  the  cells.  Hence  it  seems  probable  that  the  fat  before 
passing  through  this  part  of  the  cell  becomes  split  up  into  glycerin  and 


X'C% 


a  "^       ^    ^     O  O  O     O  O^  "-^ 

^^     f         (    0 '■^'-^""':' 
-^    ~  -  o       ®  ^   o  o    V^     ~ 


Q 


Fig.  177. — Fat  Absorption.  Longitudinal  section  of  villus  of  cat's  small  intestine, 
three  hours  after  feeding.  X3S0.  Osmic  acid,  a,  Fat  droplets  in  epithelial  cells;  b, 
fat^droplets  in  leucocytes  in  stroma;  c,  fat  droplets  in  leucocytes  within  lacteal;  d,  fat 
droplets  free  in  lacteal;  e,  capillary  containing  blood  cells;  /,  central  lacteal  of  villus. 

fatty  acids  which  are  united  again  to  form  fat  within  the  protoplasm 
of  the  cell.  Leucocytes  containing  fat  globules  are  seen  throughout 
the  stroma.  Within  the  lacteals  are  found  fat- containing  leucocytes 
and  free  fat  droplets  of  various  size.  It  would  thus  seem  probable 
that  the  process  of  fat  absorption  consists  in:  (i)  The  passage  of 
glycerin  and  fatty  acids  through  the  cell  borders;  (2)  their  reunion  in 


THE  DIGESTIVE  SYSTEIM  275 

the  cell  to  form  fat;  (3)  the  transference  of  these  fat  globules  to  leuco- 
cytes; which  (4)  carry  them  to  the  lacteals.  In  the  lacteals  the  fat  is 
probably  set  free  by  disintegration  of  the  leucocytes.  Other  fat 
droplets — perhaps  the  majority — pass  from  the  epithelial  cells  into 
the  lacteal  without  the  aid  of  leucocytes,  possibly  assisted  by  contrac- 
tions of  the  smooth  muscle  fibres. 

TECHNIC 

(i)  The  technic  for  the  small  and  large  intestines  and  rectum  is  the  same  as 
for  the  stomach.  Accurate  fixation  of  the  villi  is  difficult,  there  being  usually- 
some  shrinkage  of  the  connective  tissue  of  the  core  away  from  the  epithelium. 

A  longitudinal  section  should  be  made  through  the  junction  of  small  and  large 
intestine,  showing  the  transition  from  the  villus-covered  surface  of  the  former 
to  the  comparatively  smooth  surface  of  the  latter. 

To  show  B runner's  glands  a  section  of  the  duodenum  is  required. 

To  show  the  varying  shapes  of  the  villi  in  the  different  regions,  sections  should 
also  be   made  of  the  jejunum  and  ileum. 

Solitarj^  follicles  may  usually  be  seen  in  any  of  the  above  sections. 

A  smaU  Peyer's  patch,  together  -with,  the  entire  thickness  of  the  intestinal 
wall,  should  be  removed,  treated  as  above,  stained  with  haematoxylin-eosin 
(technic  i,  p.  20),  or  with  hcematoxylin-picro-acid-fuchsin  (technic  3,  p.  21),  and 
mounted  in  balsam. 

(2)  A  vermiform  appendix,  as  fresh  as  possible,  should  be  cut  transversely 
into  small  pieces,  fixed  in  form.alin-Muller's  fluid  (technic  5,  p.  7),  and  hardened 
in  alcohol.  Thin  transverse  sections  are  made  through  the  entire  wall,  stained 
with  haimatoxylin-eosin  or  hajmatoxylin-picro-acid-fuchsin,  and  mounted  in 
balsam. 

(3)  Fat  Absorption. — For  the  purpose  of  studying  the  process  by  which 
fat  passes  from  the  lumen  of  the  gut  into  the  chyle  vessels,  an  animal  should  be 
kiUed  at  the  height  of  fat  absorption.  A  frog  fed  with  fat  bacon  and  killed  two 
days  later,  a  dog  fed  with  fat  meat,  or  a  cat  with  cream  and  killed  after  from  four 
to  eight  hours,  furnishes  good  material.  Usually  if  the  preparation  is  to  be  suc- 
cessful, the  lumen  of  the  intestine  will  be  found  to  contain  emulsified  fat  and  the 
lacteals  of  the  mesentery  are  seen  distended  with  chyle.  Extremely  thin  slices 
of  the  mucous  membrane  of  the  small  intestine  are  fixed  in  i-per-cent.  osmic  acid 
or  in  osmium  bichromate  solution  (5-per-cent.  aqueous  solution  potassium  bi- 
chromate and  2-per-cent.  aqueous  solution  osmic  acid — equal  parts)  for  twelve 
to  twenty-four  hours,  after  which  they  are  passed  rat  her  quickly  through  graded 
alcohols.  Sections  should  be  thin  anrl  mounted,  {•illicr  unstained  or  after  a 
slight  eosin  stain,  in  glycerin. 

(4)  The  blood-vessels  of  the  stomach  arc  best  studied  in  injcc  led  specimens. 
CScc  page  25) 

The  Larger  Glands  of  the  Digestive  System 

The  smaller  tubular  glands  which  form  a  |)arr  of  the  niiK ous  mem- 
brane and  submucosa  of  the  alimentary  tract  liaxe  been  already  de- 


276  THE  ORGANS 

scribed.  Certain  larger  glandular  structures,  the  development  of 
which  is  similar  to  that  of  the  smaller  tubules  but  which  come  to  lie 
wholly  without  the  alimentary  tract,  connected  with  it  only  by  their 
main  excretory  ducts,  and  which  are  yet  functionally  an  important 
part  of  the  digestive  system,  remain  to  be  considered. 
These  are: 

[■  (a)  The  parotid. 

1.  The  salivary  glands       (&)  The  sublingual. 

L  (c)  The  submaxillary. 

2.  The  pancreas. 

3.  The  liver. 

The  Salivary  Glands 

The  salivary  glands  are  all  compound  tubular  glands.  In  man 
the  parotid  is  serous;  the  sublingual  and  submaxillary,  mixed  serous 
and  mucous  (page  221).  Only  the  general  structure  of  these  glands  is 
here  described,  the  minute  structure  of  mucous  and  serous  glands 
having  been  described  on  page  221. 

Each  gland  consists  of  gland  tissue  proper  and  of  a  supporting 
connective- tissue  framework.  The  framework  consists  of  a  connect- 
ive-tissue capsule  which  encloses  the  gland,  but  blends  externally 
with  and  attaches  the  gland  to  the  surrounding  structures.  From 
the  capsule  trabecules  pass  into  the  gland,  subdividing  it  into  lobes 
and  lobules.  The  gland  tissue  proper  consists  of  systems  of  excretory 
ducts  opening  into  secretory  tubules,  all  being  lined  with  one  or  more 
layers  of  epithelial  cells.  Each  gland  has  one  main  excretory  duct. 
This  divides  into  branches — interlobar  ducts — which  run  to  the  lobes 
in  the  connective  tissue  which  separates  them.  The  interlobar  ducts 
give  rise  to  branches  which,  as  they  pass  to  the  lobules  in  the  inter- 
lobular connective  tissue,  are  known  as  interlobular  ducts.  From 
the  latter,  branches  enter  the  lobules — intralobular  ducts — and  split 
up  into  terminal  secreting  tubules  which  constitute  the  bulk  of  the 
lobule.  As  the  smaller  intralobular  ducts  are  lined  with  cells  of  a 
secretory  type,  and  probably  take  part  in  the  elaboration  of  the 
secretion  of  the  gland,  they  have  been  called  salivary  or  secreting 
tubules.  These,  in  the  submaxillary  and  parotid  glands,  open  into 
tubules  which  have  a  narrow  lumen  and  are  lined  with  low  or  flat 
epithelium;  lying  between  the  secreting  tubules  and  the  terminal 
tubules,  they  are  known  as  intercalated  or  intermediate  tubules.     From 


THE  DIGESTIVE  SYSTEM 


27; 


the  interlobular  connective  tissue  delicate  extensions  pass  into  the 
lobules,  separating  the  gland  tubules.  The  glandular  tissue  is  known 
as  the  parenchyma  of  the  gland  in  contradistinction  to  the  connective 
or  ijiterstitial  tissue. 

The  parotid  gland  in  man,  dog,  cat,  and  rabbit  is  a  purely  serous 
gland.  Its  duct  system  is  complex.  The  main  excretory  duct 
(Stenoni)  is  lined  by  two  layers  of  columnar  epithelium  resting  upon  a 
distinct  basement  membrane.  The  main  duct  divides  into  numerous 
branches,  which  in  turn  give  rise  to  the  secreting  or  salivary  tubules. 
These  are  continuous  with  the  long  narrow  intermediate  tubules,  from 


-ra 


Fig.  178.— Diagrams  to  illustrate  the  Structure  of  the  Salivary  Glands.  (Stohr.) 
A,  Parotid;  B,  sublingual;  C,  submaxillary,  a,  Excretory  duct;  b,  secreting  tubule; 
c,  intermediate  tubule;  d,  terminal  tubule. 

each  of  which  are  given  off  a  number  of  short  terminal  tubules  (Figs. 
178,  A  and  180).  The  two-layered  epithelium  of  the  main  duct 
becomes  reduced  in  the  smaller  ducts  to  a  single  layer  of  columnar 
cells.  The  salivary  tubules  are  lined  with  high  columnar  epithelium, 
the  bases  of  the  cells  showing  distinct  longitudinal  striations.  In  the 
intermediate  tubule  the  epithelium  is  flat,  sometimes  spindle-shaped. 
The  terminal  tubules  are  lined  with  serous  cells  (page  221).  The  con- 
nective tissue  usually  contains  a  considerable  number  of  fat  cells. 

The  sublingual  gland  is  a  mixed  gland  in  man,  dog,  cat,  and 
rabbit.  '1  lie  duct  system  is  less  complex  than  in  the  parotid.  The 
main  duct  (Hartholini)  sends  off  branches  which  arc  continuous  with 


278 


THE  ORGANS 


tubules,  showing  a  few  secretory  mucous  cells.  These  open  directly 
into  the  terminal  tubules  which  are  convoluted  and  vary  greatly  in 
diameter  (Fig.  178,  B).  The  excretory  duct  is  like  that  of  the  parotid 
gland,  lined  with  a  two-layered  columnar  epithehum  resting  upon  a 
basement  membrane.  In  the  smaller  ducts  the  epithelium  is  reduced 
to  a  single  layer  of  columnar  cells.  There  are  no  intermediate 
tubules .  The  terminal  tubules  are  lined  with  both  serous  and  mucous 
cells  (page  221).  The  crescents  of  Gianuzzi  (page  222)  are  numerous 
and  large.  The  connective  tissue  of  the 
gland  contains  many  lymphoid  cells  (Fig.  181). 
Near  the  sublingual  gland  is  a  group  of 

/,  some  5  to  20  simple  tubular  glands.     Their 

I  terminal  tubules  are  lined  almost  wholly  with 

1  mucous   cells.      This  group   of  tubules  has 

been  designated  the  "sublingualis  minor." 

The  submaxillary  gland  is  also  a  mixed 
gland  in  man,  dog,  cat,  and  rabbit.  In  com- 
plexity of  its  duct  system  it  stands  between 
the  parotid  and  the  subUngual  (Fig.  178). 
The  main  duct  (Wharton's)  has  not  only  a 
two-layered  epithelial  lining  resting  upon  a 
basement  membrane,  but  is  distinguished  by 
a  richly  cellular  stroma  and  a  thin  layer  of 
longitudinally  disposed  smooth  muscle. 
Branches  of  the  main  duct  open  into  long 
secreting  tubules  which  communicate  with  the 
terminal  tubules  by  means  of  short  narrow 
intermediate  tubules  (Fig.  178,  C).  The 
secretory  tubules  are  lined  as  in  the  parotid  with  columnar  cells 
whose  bases  are  longitudinally  striated.  These  cells  usually  contain 
more  or  less  yellow  pigment.  The  intermediate  tubules  have  a 
low  cuboidal  or  flat  epithelium.  Most  of  the  end  tubules  contain 
serous  cells  only  (page  221).  The  crescents  of  the  mucous  tubules 
(page  222)  are  less  numerous  and  smaller  than  those  in  the  sublingual, 
consisting  as  a  rule  of  only  from  one  to  three  cells  (Fig.  182). 

Blood-vessels. — The  larger  arteries  run  in  the  connective-tissue 
septa  with  the  ducts,  giving  off  branches  which  accompany  the  divi- 
sions of  the  ducts  to  the  lobules,  where  they  break  up  into  capillary 
networks  among  the  tubules.  These  give  rise  to  veins  which  accom- 
pany the  arteries. 


Fig.  179. — Reconstructed 
Model  of  Small  Muco-serous 
Gland.  Dotted  parts  corre- 
sponding to  the  "crescents". 
(Maziarski). 


THE  DIGESTIVE  SYSTEIM 


% 


279 


M 


^'^  ::■■;/ -On 


Intercalated 
.  tubule 


Fat  cells 


Terminal  tubule 


Fig.   i8o. — Section  of  Human  Parotid  Gland.     X252.    (Stohr.)    The  narrow  lumina 
of  the  terminal  tubules  do  not  show  in  this  figure. 


f^    ^>J^»     0  ^-^ 


■  ■» 
ft 


Fig.  181.— Section  of  Human  Sublingual  Gland.  X2S2.  (Stohr.)  a,  Excretory 
duct;  h,  lumina  of  serous  and  mucous  tubules;  c,  mucous  tubule;  d,  demilune;  e,  serous 
tubule;  /,  cross  section  mucous  tubule;  g,  interstitial  connective  tissue. 


280 


THE  ORGANS 


The  l3miphatics  begin  as  minute  capillaries  in  the  connective 
tissue  separating  the  terminal  tubules.  These  empty  into  larger 
lymph  vessels  which  accompany  the  arteries  in  the  septa. 

The  nerves  of  the  salivary  glands  are  derived  from  both  cerebro- 
spinal and  sympathetic  systems,  and  consist  of  both  medullated  and 
non-medullated  fibres.  The  medullated  fibres  are  afferent,  probably 
the  dendrites  of  cells  located  in  the  geniculate  ganglion.  Small 
bundles  of  these  fibres  accompany  the  ducts.     Single  fibres  leave  the 


Fig.  182. — Section  of  Human  Submaxillary  Gland.  X252.  (Stohr.)  a,  Mucous 
tubule;  b,  serous  tubule;  c,  intermediate  tubule;  d,  "secretory"  tubule;  e,  demilune;/, 
lumen;  g,  interstitial  connective  tissue. 


bundles,  lose  their  medullary  sheaths,  and  form  a  non-medullated 
subepithehal  plexus,  from  which  delicate  fibrils  pass  to  end  freely 
among  the  epithelial  cells.  Efferent  impulses  reach  the  gland  through 
the  sympathetic.  The  fibres  are  axones  of  cells  situated  in  small 
peripheral  ganglia;  the  cells  sending  axones  to  the  submaxillary 
lying  upon  the  main  excretory  duct  and  some  of  its  larger  branches; 
those  sending  axones  to  the  sublingual  being  situated  in  a  small  gang- 
lion— the  sublingual — lying  in  the  triangular  area  bounded  by  the 
chorda  tympani,  the  lingual  nerve,  and  Wharton's  duct;  those  sup- 
plying the  parotid  probably  being  in  the  otic  ganglion.  Axones 
from  these  cells  enter  the  glands  with  the  excretory  duct  and  follow 
its  branchings  to  the  terminal  tubules,  where  they  form  plexuses 


THE  DIGESTIVE  SYSTEM  281 

beneath  the  epitheHum.  From  these,  terminals  pass  to  the  secreting 
cells.  It  is  probable  that  the  saHvary  glands  also  receive  sympathetic 
fibres  from  cells  of  the  superior  cervical  ganglia. 

TECHNIC 

(i)  The  salivar)^  glands  should  be  fixed  in  Flemming's  fluid  (technic  7,  p.  7), 
or  in  formalin- JNIiiller's  fluid  (technic  5,  p.  7).  Sections  are  cut  as  thin  as  possi- 
ble, stained  with  haematoxylin-eosin  (technic  i,  p.  20),  and  mounted  in  balsam. 

(2)  For  the  study  of  the  secretory  activities  of  the  gland  cells,  glands  from  a 
fasting  animal  should  first  be  examined  and  then  compared  with  those  of  a  gland 
the  secretion  of  which  has  been  stimulated  by  the  subcutaneous  injection  of  pilo- 
carpine. Fix  in  Flemming's  or  in  Zenker's  fluid  (technic  9,  p.  8).  Examine 
some  sections  unstained  and  mounted  in  glycerin,  others  stained  with  hasma- 
toxylin-eosin  and  mounted  in  balsam. 

(3)  The  finer  intercellular  and  intracellular  secretory  tubules  are  demon- 
strated by  Golgi's  method.  Small  pieces  of  absolutely  fresh  gland  are  placed 
for  three  days  in  osmium-bichromate  solution  (3-per-cent.  potassium  bichromate 
solution,  4  volumes;  i-per-cent.  osmic  acid,  i  volume),  and  then  transferred  with- 
out washing  to  a  o.7S-per-cent.  aqueous  solution  of  silver  nitrate.  Here  they 
remain  for  from  two  to  four  days,  the  solution  being  frequently  changed.  The 
processes  of  dehydrating  and  embedding  should  be  rapidly  done,  and  sections 
mounted  in  glycerin,  or,  after  clearing  in  xylol,  in  hard  balsam. 

Pancreas 

The  pancreas  is  a  compound  tubular  gland.  While  in  general 
similar  to  the  salivary  glands,  it  has  a  somewhat  more  complicated 
structure.  A  connective-tissue  capsule  surrounds  the  gland  and 
gives  off  trabeculae  which  pass  into  the  organ  and  divide  it  into  lobules. 

In  some  of  the  lower  animals,  as  for  example  the  cat,  these  lobules 
are  well  defined,  being  completely  separated  from  one  another  by 
connective  tissue.  In  this  respect  they  resemble  the  lobules  of  the 
pig's  liver.  A  number  of  these  primary  lobules  are  grouped  together 
and  surrounded  by  connective  tissue,  which  is  considerably  broader 
and  looser  in  structure  than  that  separating  the  primary  lobules. 
These  constitute  a  lobule  group  or  secondary  lobule. 

In  the  human  j)ancreas  the  division  into  lobules  and  lobule  groups 
is  much  less  distinct,  although  it  can  usually  be  made  out.  This  is 
due  to  the  incompleteness  of  the  connective-tissue  septa,  the  human 
pancreas  in  this  respect  resembling  the  liuman  liver.  Rarely  the 
human  pancreas  is  distinctly  l()])ulated. 

The  gland  has  a  main  excretory  duct,  the  pancreatic  duct  or  dud 
of  Wirsung.     In  many  cases  there  is  also  a  secondary  excretory  dud, 


282 


THE  ORGANS 


the  accessory  pancreatic  duct  or  duct  of  Santorini.  Both  open  into 
the  duodenum.  The  main  duct  extends  almost  the  entire  length  of 
the  gland,  giving  ofif  short  lateral  branches,  one  of  which  enters  the 
centre  of  each  lobule  group.  Here  it  splits  up  into  branches  which 
pass  to  the  primary  lobules.     From  these  intralobular  ducts  are  given 

off  long,  narrow,  intermediate  tubules,  which 
in  turn  give  rise  to  the  terminal  secreting 
tubules  (Fig.  183). 

The  excretory  ducts  are  lined  with  a  simple 
high  columnar  epitheHum  which  rests  upon 
a  basement  membrane.  Outside  of  this  is  a 
connective-tissue  coat,  the  thickness  of  which 
is  directly  proportionate  to  the  size  of  the 
duct.  In  the  pancreatic  duct  goblet  cells  are 
present,  and  the  accompanying  connective 
tissue  of  the  main  duct  and  of  its  larger 
branches  contains  small  mucous  glands.  As 
the  ducts  decrease  in  size,  the  epitheHum  be- 
comes lower  until  the  intermediate  tubule  is 
reached  where  it  becomes  fiat. 

The  terminal  tubules  themselves  are  most 
of  them  very  short,  frequently  almost  spher- 
ical. This  and  the  fact  that  several  terminal 
tubules  are  given  off  from  the  end  of  each  in- 
termediate tubule  have  led  to  the  description 
of  these  tubules  as  alveoli,  and  of  the  pancreas 
as  a  tubulo-alveolar  gland,  although  there  is 
no  dilatation  of  the  lumen.  The  terminal  tubules  are  lined  with  an 
irregularly  conical  epithelium  resting  upon  a  basement  membrane 
(Figs.  184  and  185).  The  appearance  of  these  cells  depends  upon 
their  functional  condition.  Each  cell  consists  of  a  central  zone 
bordering  the  lumen,  which  contains  numerous  granules  known  as 
zymogen  granules,  and  of  a  peripheral  zone  next  to  the  basement 
membrane,  which  is  homogeneous  and  contains  the  nucleus  (Fig. 
185).  The  zymogen  granules  are  quite  large  granules  and  as 
they  are  highly  refractive  stand  out  distinctly  even  in  the  fresh, 
unstained  condition  and  under  low  magnification.  The  relative 
size  of  these  zones  depends  upon  whether  the  cell  is  in  the 
active  or  resting  state  (compare  Fig.  186,  A  and  B).  During  rest 
(fasting)  the  two  zones  are  of  about  equal  size.     During  the  early 


c 
Fig.  183. — Diagram  to 
illustrate  Structure  of  Pan- 
creas. (Stohr.)  a,  Excretory 
duct;  b,  intermediate  tubule; 
c,  c,  terminal  tubules. 


THE  DIGESTIVE  SYSTEM 


283 


stages  of  activity  (intestinal  digestion)  the  granules  largely  disappear 
and  the  clear  zone  occupies  almost  the  entire  cell.  During  the  height 
of  ^digestion  the  granules  are  increased  in  number  to  such  an  extent 


^^f^^^^ 


^^SA 


Fig.  184. — Section  of  Human  Pancreas.  X112.  (Kolliker.)  af,  Alveoli;  a,  inter- 
lobular duct  surrounded  by  interlobular  connective  tissue;  L,  islands  of  Langerhans;  -a, 
small  vein. 

that  they  almost  fill  the  cell,  while  after  prolonged  secretion  they  are 
again  almost  absent.  The  cell  now  returns  to  the  resting  state  in 
which  the  two  zones  are  about  equal.  The  increase  and  disappear- 
ance of  the  granules  are 
marked  by  the  appearance  of 
the  fluid  secretion  of  the 
gland  in  the  lumen.  It  would 
thus  seem  probable  that  the 
zymogen  granules  are  the 
intracellular  representatives 
of  the  secretion  of  the  gland. 
In  sections  of  the  gland 
there  are  seen  within  the 
lumina  of  many  of  the  secret- 
ing tubules  one  or  more  small 
cells  of  which  little  but  the 
nucleus  can  usually  be  made 
out.  These  cells  lie  in  contact  with  the  secreting  cells,  and  resemble 
the  flat  cells  which  line  the  intermediate  tubule.  They  arc  known 
as  the  centro-acinar  icenlro-luhular)  cells  of  Langerhans  (Fig.  185,  c). 


Fig.  185. — From  Section  of  Human  Pancreas. 
X700.  (KoUiicer.)  a,  Gland  cell;  6,  basement 
membrane;  s,  intermediate  tubule;  c,  centro- 
acinar  cells;  sk,  intracellular  secretory  tubule. 


284 


THE  ORGANS 


Their  significance  is  not  definitely  known.  Langerhans  believed 
that  they  were  derived  from  the  intermediate  tubule,  the  epithe- 
lium  of  which,  instead  of   directly  joining   that  of    the   terminal 


Fig.  i86. — Sections  of  Alveoli  from  Rabbit's  Pancreas.  (Foster,  after  Kiihne  and 
Lea.)  A,  Resting  alveolus,  the  inner  zone  (a),  containing  zymogen  granules,  occupying 
a  little  more  of  the  cell  than  the  outer  clear  zone  (b);  c,  indistinct  lumen.  B,  Active 
alveolus,  granules  coarser,  fewer,  and  confined  to  inner  ends  of  the  cell  (a),  the  outer 
clear  zone  (b)  being  much  larger;  outlines  of  cells  and  of  lumen  much  more  distinct. 

tubule  as  in  the  submaxillary  gland,  was  continued  over  into  the 
lumen  of  the  terminal  tubule  (Fig.  185).  This  interpretation  has 
been  quite  generally  accepted. 

Cells  which  differ  from  the  secreting  cells  are  frequently  found 


Fig.  187. — Sections  through  AlveoU  of  Human  Pancreas — Golgi  Method — (Dogiel), 
to  show  intracellular  secretory  tubules,  a,  Intermediate  tubule  giving  off  several 
terminal  tubules,  from  which  pass  off  minute  intracellular  secretory  tubules;  b,  gland 
cells  lining  terminal  tubules. 

wedged  in  between  the  latter.     They  extend  from  the  lumen  to  the 
basement  membrane  and  are  probably  sustentacular . 

Passing  from  the  lumen  of  the  terminal  tubule,  sometimes  between 
the  centro-tubular  cells,  directly  into  the  cytoplasm  of  the  secreting 


THE  DIGESTIVE  SYSTEjM 


285 


cells  are  minute  intracellular  secretory  tubules.     These  are  demonstra- 
ble only  by  special  methods  (Golgi)  (Fig.  187). 

The  pancreas  also  contains  pecuHar  groups  of  cells,  the  cell-islands 
of  Langerhans,  having  a  diameter  from  200  to  300/^  (Figs.  184,  188, 
and  189).  The  "island"  cells  differ  quite  markedly  both  in  arrange- 
ment and  structure  from  those  which  line  the  terminal  tubules  (Fig. 
188),  They  contain  no  zymogen  granules.  They  are  arranged  in 
anastomosing  cords  or  strands  which  are  separated  from  one  another 
by  capillaries.  There  are  no  ducts  and  the  method  of  Golgi  shows  no 
inter-  or  intra-cellular  secretory  tubules.     Their  protoplasm  is  un- 


© 


,^- 


FiG.  188. — Island  of  Langerhans  and  few  surrounding  Pancreatic  Tubules.     (Bohm  and 
von  DavidofT.)     a,  Capillary;  b,  tubule. 

stained  by  basic  dyes,  but  stains  homogeneously  with  acid  dyes. 
Their  nuclei  vary  greatly  in  size,  some,  especially  where  the  cells  are 
closely  packed,  being  small,  others  being  large  and  vesicular.  Some 
of  the  islands  are  quite  sharply  outlined  by  delicate  fibrils  of  connec- 
tive tissue  containing  a  few  elastic  fibres  (Fig.  188).  Others  blend 
with  the  surrounding  tis.sucs. 

The  origin,  structure,  and  function  of  these  islands  have  been  subjects  of 
much  controversy.  For  some  time  they  were  considered  of  lymjjhoid  origin. 
They  are  now  believed  to  be  epithelial  tells  having  a  develo[)mental  history 
similar  to  the  cells  lining  the  secreting  lubules.     Each  cell-island  consists  of, 


286 


THE  ORGANS 


in  addition  to  the  cells,  a  tuft  or  glomerulus  of  broad  tortuous  anastomosing 
capillaries,  which  arise  from  the  network  of  capillaries  surrounding  the  secret- 
ing tubules.  The  close  relation  of  cells  and  capillaries  and  the  absence  of  any 
ducts  have  led  to  the  hypothesis  that  these  cells  furnish  a  secretion — internal 
secretion — ^^which  passes  directly  into  the  blood-vessels. 

In  a  recent  publication  Opie  reviews  previous  work  upon  the  histology  of  the 
pancreas  and  adds  the  results  of  his  own  careful  researches.  He  concludes  that 
the  cell-islands  of  Langerhans  are  definite  structures  "formed  in  embryological 
life,"  that  "they  possess  an  anatomical  identity  as  definite  as  the  glomeruli  of 
the  kidney  or  the  Malpighian  body  of  the  spleen,  and  that  they  subserve  some 


Fig.  189. — From  Section  of  Pancreas,  the  blood-vessels  of  which  had  been  injected 
(Ktihne  and  Lea),  showing  island  of  Langerhans  with  injected  blood-vessels,  surrounded 
by  sections  of  tubules.     Zymogen  granules  are  distinct  in  inner  ends  of  cells. 

special  function."  He  calls  attention  to  the  similarity  which  Schafer  noted 
between  these  cell-islands  and  such  small  ductless  structures  as  the  carotid  and 
coccygeal  glands  and  the  parathyreoid  bodies.  From  his  study  of  the  pancreas 
in  diabetes,  Opie  concludes  that  the  islands  of  Langerhans  are  concerned  in 
carbohydrate  metabolism. 

Blood-vessels. — The  arteries  enter  the  pancreas  with  the  main 
duct  and  break  up  into  smaller  arteries  which  accompany  the  smaller 
ducts.  These  end  in  a  capillary  network  among  the  secreting  tubules. 
From  this,  venous  radicles  arise  which  converge  to  form  larger  veins. 
These  pass  out  of  the  gland  in  company  with  the  arteries. 

Lymphatics. — Of  the  lymphatics  little  is  known. 

Nerves. — The  nerves  are  almost  wholly  from  the  sympathetic 
system,  and  are  non-medullated.  Some  of  them  are  axones  of  cells 
in  sympathetic  gangHa,  outside  the  pancreas;  others,  of  cells  situated 
in  small  ganglia  within  the  substance  of  the  gland.  They  pass  to 
plexuses  among  the  secreting  tubules,  to  which  and  to  the  walls 
of  the  vessels  they  send  dehcate  terminal  fibrils. 


THE  DIGESTIVE  SYSTE:M 


287 


TECHNIC 

(i)  The  general  technic  for  the  pancreas  is  the  same  as  for  the  salivary- 
glands  (page  281). 

(2)  Zymogen  granules  may  be  demonstrated  by  fixation  in  formalin-Miil- 
ler's  fluid  (technic  5,  p.  7),  and  staining  with  picro-acid-fuchsin  (technic  2,  p. 
20),  or  with  Heidenhain's  iron  haematoxylin  (technic  3,  p.  18). 

(3)  The  arrangement  of  the  blood-vessels  in  the  islands  of  Langerhans  may 
be  studied  in  specimens  in  which  the  vascular  system  has  been  injected  (page  25) . 

The  Liver 

The  Hver  is  a  compound  tubular  gland,  the  secreting  tubules  of 
which  anastomose.  There  are  thus,  strictly  speaking,  no  "terminal 
tubules"  in  the  liver,  the  lumina  and  walls  of  neighboring  tubules 
anastomosing  without  any  distinct  line  of  demarcation. 


Fic.  190. — Section  of  Lobule  of  Pig's  Liver  X60  (technic  i,  p.  295),  showing  lohulc 
completely  surrounded  by  connective  tissue,  a,  Portal  vein;  b,  bile  duct;  c,  hepatic 
artery;  d,  [wirtal  canal;  e,  capillaries;/,  central  vein;  /j,  cords  of  liver  cells;  //,  hepatic  vein. 

The  liver  is  surrounded  by  a  connective-tissue  capsule,  the  capsule 
oJGlisson.  At  the  liilurn  tliis  capsule  extends  deep  into  the  substance 
of  the  hver,  giving  off  broad  connective-tissue  sepia,  which  divide  the 
organ  into  lobes.     I*>om  the  capsule  and  from  these  interlobar  septa, 


288  THE  ORGANS 

trabeculae  pass  into  the  lobes,  subdividing  them  into  lobules.  In  some 
animals,  as  for  example  the  pig,  each  lobule  is  completely  invested  by 
connective  tissue  (Fig.  190).  In  man,  only  islands  of  connective 
tissue  are  found,  usually  at  points  where  three  or  more  lobules  meet 
(Fig.  191).  The  lobules  are  cylindrical  or  irregularly  polyhedral  in 
shape,  about  i  mm.  in  breadth  and  2  mm.  in  length.  Excepting 
just^beneath  the  capsule,  where  they  are  frequently  arranged  with 

B  P     H 

I,  '  -'.  '  -  '-,  '*   **  ^^\  •">  «  '\V  /l  ^/-   °°  ^'.''/''°°/<'  '  «  i'  •"  \f'"--^  ,    i* 


.«? 


Fig.  191. — Section  of  Human  Liver.  X80.  (Hendrickson.)  P,  Portal  vein;  R, 
hepatic  artery;  B,  bile  duct.  P,  H,  B  constitute  the  portal  canal  and  lie  in  the  connec- 
tive tissue  between  the  lobules. 

their  apices  toward  the  surface,  the  liver  lobules  have  an  irregular 
arrangement. 

The  lobule  (Fig.  190)  which  may  be  considered  the  anatomic  unit 
of  structure  of  the  liver,  consists  of  secreting  tubules  arranged  in  a 
definite  manner  relatively  to  the  blood-vessels.  The  blood-vessels 
of  the  liver  must  therefore  be  first  considered. 

The  BLOOD  SUPPLY  of  the  liver  is  peculiar  in  that  in  addition  to  the 
ordinary  arterial  supply  and  venous  return,  which  all  organs  possess, 


THE  DIGESTIVE  SYSTEM 


289 


the  liver  receives  venous  blood  in  large  quantities  through  the  portal 
vein.  There  are  thus  hco  afferent  vessels,  the  hepatic  artery  and  the 
portal  vein,  the  former  carrying  arterial  blood,  the  latter  venous 
blood  from  the  intestine.  Both  vessels  enter  the  liver  at  the  hilum 
and  divide  into  large  interlobar  branches,  which  follow  the  connective- 
tissue  septa  between  the  lobes.  From  these  are  given  off  interlobular 
branches,  which  run  in  the  smaller  connective-tissue  septa  between 
the  lobules.  From  the  interlobular 
branches  of  the  portal  vein  arise  veins 
which  are  still  interlobular  and  encircle 
the  lobules.  These  send  off  short 
branches  which  pass  to  the  surface  of 
the  lobule,  where  they  break  up  into 
a  rich  intralobular  capillary  network. 
These  intralobular  capillaries  all  con- 
verge toward  the  center  of  the  lobule, 
where  they  empty  into  the  central  vein 
(Fig.  190).  The  central  veins  are  the 
smallest  radicles  of  the  hepatic  veins, 
which  are  the  efferent  vessels  of  the 
hver.  Each  central  vein  begins  at  the 
apex  of  the  lobule  as  a  small  vessel  little 
larger  than  a  capillary.  As  it  passes 
through  the  centre  of  the  long  axis  of 
the  lobule  the  central  vein  constantly 
receives  capillaries  from  all  sides,  and, 
increasing  in  size,  leaves  the  lobule  at 
its  base.  Here  it  unites  with  the  central  veins  of  other  lobules  to 
form  the  sublobular  vein  which  is  a  branch  of  the  hepatic  (Fig.  198). 

The  hepatic  artery  accompanies  the  portal  vein,  following  the 
branchings  of  the  latter  through  the  interlobar  and  interlobular  con- 
nective tissue,  where  its  finer  twigs  break  up  into  capillary  networks. 
Some  of  these  capillaries  empty  into  the  smaller  branches  of  the  portal 
vein;  others  enter  the  lobules  and  anastomose  with  the  intralobular 
portal  capillaries. 

'J'he  M/\iN  p:xcretory  Duci'—hepatic  duct — leaves  the  liver  at  the 
hilum  near  the  entrance  of  the  portal  vein  and  hepatic  artery.  Within 
the  liver  the  duct  divides  and  subdivides,  giving  off  interlobar,  and 
these  in  turn  interlobular  branches.  These  ramify  in  the  connective 
tissue,  where  they  always  accompany  the  branches  of  the  jjortal  vein 


Fig.  192. — Portal  Canal.  X315. 
(Klein  and  Smith.)  a,  Hepatic 
artery;  F,  portal  vein;  6,  bile  duct. 


290 


THE  ORGANS 


and  hepatic  artery.  These  three  structures — the  hepatic  artery,  the 
portal  vein,  and  the  bile  duct,  which  always  occur  together  in  the  con- 
nective tissue  which  marks  the  point  of  separation  of  three  or  more 
lobules — together  constitute  the  portal  canal  (Fig.  192).  From  the 
interlobular  ducts  short  branches  pass  to  the  surfaces  of  the  lobules. 
From  these  are  given  off  extremely  narrow  tubules,  which  enter  the 
lobule  as  intralobular  secreting  tubules. 

The  walls  of  the  ducts  consist  of  a  single  layer  of  epithelial  cells 
resting  upon  a  basement  membrane  and  surrounded  by  connective 


Fig.  193. — Part  of  Lobule  of  Human  Liver,  showing  capillaries  and  anastomosing  cords 
of  liver  cells.      X350.     a,  Liver  cells;  b,  capillaries. 

tissue  (Fig.  192).  The  height  of  the  epithelium  and  the  amount  of 
connective  tissue  are  directly  proportionate  to  the  size  of  the  duct. 
In  the  largest  ducts  there  are  usually  a  few  scattered  smooth  muscle 
cells.  The  walls  of  the  secreting  tubules  are  formed  by  the  liver  cells. 
The  LIVER  CELLS  (Fig.  193)  are  irregularly  polyhedral  in  shape. 
They  have  a  granular  protoplasm  which  frequently  contains  gly- 
cogen, pigment  granules,  and  droplets  of  fat  and  bile.  Each  cell 
contains  one  or  more  spherical  nuclei.  Like  other  gland  cells,  the 
granularity  of  the  protoplasm  depends  upon  its  functional  condition. 
Within  the  cells  are  minute  irregular  canals,  some  of  which  can  be 


THE  DIGESTIVE  SYSTE.M 


291 


injected   through   the    blood-vessels,   while   others   are   apparently 
continuous  with  the  secreting  tubules  (Fig.  195,  A  and  B). 

The  capillaries  of  the  portal  vein,  as  they  anastomose  and  con- 
verge from  the  periphery  to  the  centre  of  the  lobule,  form  long-meshed 


Fig.  194. — Part  of  Lobule  of  Human  Liver,  Golgi  Method  (technic  3,  p.  295),  to 
show  relations  of  bile  duct  to  intralobular  secretory  tubules  and  of  the  latter  to  the  liver 
cells,  a,  Bile  duct;  b,  cords  of  liver  cells;  c,  blood  capillaries;  d,  central  vein;  e,  secretory- 
tubules. 

capillary  networks.  In  the  meshes  of  this  network  lie  the  anasto- 
mosing secreting  tubules.  On  account  of  the  shape  of  the  capillary 
network,  the  liver  cells,  which  form  the  walls  of  these  tubules,  are 


Fig.  195. — A,  Cell  from  human  liver  showing  intracellular  canals  (Browicz);  c,, 
intracellular  canal;  n,  nucleus.  Ji,  From  section  of  rabbit's  liver  injected  'jirough  portal" 
vein,  showing  intracellular  canals  (continuous  with  inten  cllular  blood  ca|)illaries). 
(Schafer.) 

arranged  in  anastomosing  rows  or  ( ords,  known  as  hcpalic  cords  or 
cords  of  liver  cells  (Fig.  193). 

The  secreting  tubules  (Fig.  194)  are  extremely  minute  channels, 
the  walls  of  which  are  the  liver  cells.     A  secretory  lubulc  always  runs, 


292 


THE  ORGANS 


between  two  contiguous  liver  cells,  in  each  of  which  a  groove  is  formed. 
The  Uood  capillaries,  on  the  other  hand,  are  found  at  the  corners  where 
three  or  more  Uver  cells  come  in  contact.  It  thus  results  that  bile 
tubules  and  blood  capillaries  rarely  lie  in  contact,  but  are  regularly- 
separated  by  part  of  a  liver  cell.  Exceptions  to  this  rule  sometimes 
occur.  While  most  of  the  secretory  tubules  anastomose,  some  of 
them  end  blindly  either  between  the  liver  cells  or,  in  some  instances, 
after  extending  a  short  distance  within  the  cell  protoplasm  (Fig.  195, 
A).     At  the  surface  of  the  lobula.there  is  a  modification  of  some  of 


Fig.  196. — Liver  Lobule,  to  show  Connective-tissue  Framework.     (Mall.) 


the  liver  cells  to  a  low  cuboidal  type,  and  these  become  continuous 
with  the  lining  cells  of  the  smallest  bile  ducts,  the  secretory  tubule 
being  continuous  with  the  duct  lumen. 

Special  methods  of  technic  have  demonstrated  a  connective- tissue 
framework  within  the  lobule.  This  consists  of  a  reticulum  of  ex- 
tremely delicate  fibrils  which  envelop  the  capillary  blood-vessels,  and 
of  a  smaller  number  of  coarser  fibres  which  radiate  from  the  region 
of  the  central  vein — radiate  fibres  (Fig.  196). 

Special  technical  methods  also  show  the  presence  of  stellate 
cells — cells  of  Kupfer — within  the  lobule.     These  are  interpreted 


THE  DIGESTIVE  SYSTE^NI 


293 


by  Kupflfer  as  belonging  to  the  endothelium  of  the  intralobular 
capillaries. 

Comparing  the  Uver  ^Nath  other  compound  tubular  glands,  it  is 
seen  to  present  certain  marked  peculiarities  which  distinguish  it  and 
which  make  its  structure  as  a  compound  tubular  gland  difficult  to 
understand.  The  most  important  of  these  are  the  following:  (Figs. 
197  and  198). 

The  extremely  small  amount  of  connective  tissue;  in  the  human 
liver  not  enough  interlobular  connective  tissue  to  outhne  the  lobules, 


_  e 


Fig.  197.  Fig.  iq8. 

Fig.  197. — Scheme  of  an  Ordinary  Compound  Tubular  Gland.  In  lobule  3  only  the 
ramifications  of  the  excretory  duct,  without  endpieces,  arc  shown.  (Stohr.)  a, 
Branches  of  excretory  duct;  b,  artery;  c,  vein;  d,  terminal  tubules;  e,  capillaries. 

Fig.  198. — Scheme  of  Liver.  In  lobule  r,  only  the  direction  of  the  endpieces  is  shown; 
in  lobule  2  only  their  branching;  in  3  only  the  excretory  ducts.  (Stohr.)  a,  Branches  of 
excretory  duct;  b,  i)ortal  vein;  c,  terminal  tubules  (hepatic  cords);  d,  capillaries;  e,  vein 
(central  and  sublobular). 

while  intralobular  connective  tissue  demon.strable  by  ordinary  stain- 
ing methods  is  wholly  absent.  There  is  thus  no  connective  tissue 
seen  separating  the  cells  of  one  tul)ulc  from  those  of  another  as,  for 
example,  in  such  a  gland  as  the  submaxillary.  The  result  is  that  cells 
of  neighboring  tubules  lie  sicle  by  side,  and  back  to  back  as  it  were, 
with  no  intervening  connective  tissue. 

The  fact  that  unlike  the  tubules  of  other  glands,  the  liver  tubule  con- 
sists of  only  two  rows  of  cells,  between  which  lies  the  lumen.  The 
latter  is  thus  never  in  touch  with  more  than  two  cells. 


294  THE  ORGANS 

The  end-to-end  anastomosis  of  the  secreting  tubules,  there  being 
jio  true  terminal  tubules;  anastomosis  of  neighboring  tubules  by 
tneans  of  side  branches ;  the  arrangement  of  the  bile  capillaries  in  such 
a  manner  that  a  single  liver  cell  abuts  upon  more  than  one  capillary. 

The  more  intimate  relation  of  the  liver  cell  to  the  blood  capillaries . 
Thus  most  gland  cells  have  one  side  on  the  lumen,  one  side  only  in 
contact  with  a  capillary  blood-vessel,  the  remaining  sides  being  in 
contact  with  other  cells  of  the  same  tubule.  A  hver  cell,  on  the 
other  hand,  may  and  usually  does  come  in  contact  with  several  blood 
capillaries. 

The  arrangement  of  both  blood-vessels  and  tubules  within  the  lobule. 
In  the  submaxillary,  for  example,  the  terminal  tubules  are  con- 
voluted and  run  in  all  directions.  In  the  liver  the  terminal  tubules 
are  straight  and  run  in  a  definite  direction  from  the  periphery  of  the 
lobule  toward  the  centre.  Again,  while  in  other  glands  both  intra- 
lobular arteries  and  ducts  are  distributed  outward  from  the  centre  of 
the  lobule,  and  the  blood  is  returned  through  veins  which  pass  to 
the  periphery  of  the  lobule,  in  the  liver  the  interlobular  ducts  pass  to 
the  periphery  of  the  lobule  and  give  off  secreting  tubules  which  pass 
in  toward  the  centre  of  the  lobule.  The  afferent  vessels  also  (portal 
veins)  take  the  blood  to  the  periphery  of  the  lobule  and  distribute 
it  to  a  capillary  network  which  converges  to  an  efferent  vessel 
(hepatic  vein)  at  the  centre  of  the  lobule.  The  veins  are  also  pecu- 
liar in  that  they  do  not  follow  the  arteries  in  leaving  the  liver  but 
pursue  an  entirely  independent  course. 

Blood-vessels. — These  have  been  already  described. 

Lymph  vessels  form  a  network  in  the  hver  capsule.  These  com- 
municate with  deep  lymphatics  in  the  substance  of  the  organ.  The 
latter  accompany  the  portal  vein  and  follow  the  ramifications  of  its 
capillaries  within  the  lobule  as  far  as  the  central  vein. 

The  nerves  of  the  liver  are  mainly  non-medullated  axones  of 
sympathetic  neurones.  The  nerves  accompany  the  blood-vessels 
and  bile  ducts,  around  which  they  form  plexuses.  These  plexuses 
give  off  fibrils  which  end  on  the  blood-vessels,  bile  ducts,  and  liver 
cells. 

Three  main  ducts,  all  parts  of  a  single  excretory  duct  system,  are 
concerned  in  the  transportation  of  the  bile  to  the  intestine,  the  hepatic, 
the  cystic,  and  the  common.  Their  walls  consist  of  a  mucous  membrane, 
a  submucosa,  and  a  layer  of  smooth  muscle.  The  mucosa  is  composed 
of  a  simple  columnar  epithehum  resting  upon  a  basement  membrane 


THE  DIGESTIVE  SYSTEM  295 

and  a  stroma  which  contains  smooth  muscle  cells  and  small  mucous 
glands.  The  suhmucosa  is  a  thin  layer  of  connective  tissue.  Hen- 
drickson  describes  the  muscular  coat  as  consisting  of  three  layers,  an 
inner  circular,  a  middle  longitudinal,  and  an  external  oblique.  At 
the  entrance  of  the  common  bile  duct  into  the  intestine,  and  at  the 
junction  of  the  duct  of  Wirsung  with  the  common  duct,  there  are 
thickenings  of  the  circular  fibres  to  form  sphincters.  In  the  cystic 
duct  occur  folds  of  the  mucosa — the  Heisterian  valve — into  which 
the  muscularis  extends. 

The  Gall-Bladder 

The  wall  of  the  gall-bladder  consists  of  three  coats — mucous, 
muscular,  and  serous. 

The  mucous  membrane  is  thrown  up  into  small  folds  or  rugcs, 
which  anastomose  and  give  the  mucous  surface  a  reticular  appearance. 
The  epithehum  is  of  the  simple  columnar  variety  with  nuclei  situated 
at  the  basal  ends  of  the  cells.  A  few  mucous  glands  are  usually  found 
in  the  stroma. 

The  muscular  coat  consists  of  bundles  of  smooth  muscle  cells 
which  are  disposed  in  a  very  irregular  manner,  and  are  separated  by 
considerable  fibrous  tissue.  A  richly  vascular  layer  just  beneath  the 
stroma  is  almost  free  from  muscle  and  corresponds  to  a  submucosa. 
It  frequently  contains  small  lymph  nodules. 

The  serous  coat  is  a  reflection  of  the  peritoneum. 

TECHNIC 

(i)  Before  taking  up  the  study  of  the  human  liver,  the  liver  from  one  of  the 
lower  animals  in  which  each  lobule  is  completely  surrounded  by  connective  tissue 
should  be  studied.  Fix  small  pieces  of  pig's  liver  in  formalin-Muller's  fluid 
(technic  5,  p.  7).  Cut  sections  near  and  parallel  to  the  surface.  Stain  with  ha^m- 
aloxylin-picro-acid-fuchsin  (technic  3,  p.  21)  and  mount  in  balsam.  In  the  pig's 
liver  the  lobules  arc  completely  outlined  by  connective  tissue  and  the  yellow 
picric-acid-stained  lobules  are  in  sharp  contrast  with  the  red  fuchsin-staincd 
connective  tissue. 

(2)  For  the  study  of  the  human  liver  treat  small  pieces  of  perfectly  fresh 
tissue  in  the  same  manner  as  the  preceding,  but  slain  with  hiumatoxylin-eosin 
(technic  i,  p.  20). 

(3)  The  secretory  tubules  and  smaller  bile  ducts  may  be  demonstrated  by 
technic,  5.  p.  2q.     .\  light  eosin  stain  brings  oul  the  liver  cells. 

(4)  For  the  study  of  the  blood-vessels  of  the  liver,  inject  the  vessels  through 
the  inferior  vena  cava  or  portal  vein.     If  the  vena  cava  is  used,  it  is  convciiicnl  to 


296  THE  ORGANS 

inject  from  the  heart  directly  through  the  right  auricle  into  the  vena  cava. 
Sections  should  be  rather  thick  and  may  be  stained  with  eosin,  or  even  lightly 
with  h^matoxyhn-eosin  (technic  i,  p.  20),  and  mounted  in  balsam. 

(5)  For  demonstrating  the  intralobular  connective  tissue,  Oppel  recommends 
fixing  fresh  tissue  in  alcohol,  placing  for  twenty-four  hours  in  a  0.5-per-cent. 
aqueous  solution  of  yellow  chromate  of  potassium,  washing  in  very  dilute  silver 
nitrate  solution  (a  few  drops  of  0.75-per-cent.  solution  to  50  c.c.  of  water)  and 
then  transferring  to  0.75-per-cent.  silver  nitrate  solution,  where  it  remains  for 
twenty-four  hours.  Embed  quickly  in  celloidin.  The  best  tissue  is  usually 
found  near  the  surfaces  of  the  blocks.  A  similar  result  is  obtained  by  fixing 
fresh^ tissue  in  o .  5-per-cent.  chromic-acid  solution  for  three  days,  then  trans- 
ferring to  o .  5-per-cent.  silver  nitrate  solution  for  two  days. 

V 

Development  or  the  Digestive  System 

In  the  development  of  the  digestive  system  all  the  layers  of  the  blastoderm 
are  involved.  Mesoderm  and  entoderm  are,  however,  the  layers  most  con- 
cerned, as  the  ectoderm  is  used  only  in  the  formation  of  the  oral  and  anal 
orifices.  The  primitive  alimentary  canal  is  formed  by  two  folds  which  grow  out 
from  the  ventral  surface  of  the  embryo  and  unite  to  form  a  canal,  in  a  manner 
that  is  quite  similar  to  the  formation  of  the  neural  canal.  In  this  way  the 
primitive  gut  is  lined  with  cells  which  previously  formed  the  ventral  surface  of 
the  embryo,  i.e.,  entoderm.  A  portion  of  the  mesoderm  accompanies  the 
entoderm  in  the  formation  of  the  folds.  This  is  known  as  the  visceral  layer  of 
the  mesoderm.  The  primary  gut  is  thus  a  closed  sac  or  tube.  It  is  connected 
with  the  umbilical  vesicle,  but  has  no  connection  with  the  exterior.  These 
connections  are  formed  later  by  oral  and  anal  invaginations  of  ectoderm  which 
extend  inward  and  open  up  into  the  ends  of  the  hitherto  imperforate  gut. 
The  ends  of  the  ahmentary  tract,  including  the  oral  cavity  and  all  of  the  glands 
and  other  structures  connected  with  it,  are  of  ectodermic  origin.  The  epithelial 
lining  of  the  gut  and  the  parenchyma  of  all  glands  connected  with  it  are  derived 
from  entoderm.  The  muscle,  the  connective  tissue,  and  the  mesothelium  of 
the  serosa  are  developed  from  mesoderm. 

The  mesodermic  elements  show  little  variation  throughout  the  gut,  the 
peculiarities  of  the  several  anatomical  divisions  of  the  latter  being  dependent 
mainly  on  special  differentiation  of  the  entoderm  (epithelium).  Beneath  the 
entodermic  cells  is  a  narrow  layer  of  loosely  arranged  tissue  which  later  separates 
into  stroma,  muscularis  mucosae,  and  submucosa.  Outside  of  this  a  broader 
mesodermic  band  of  firmer  structure  represents  the  future  muscularis. 

The  stomach  first  appears  as  a  spindle-shaped  dilatation  about  the  end  of 
the  first  month.  Its  entodermic  cells,  which  had  consisted  of  a  single  layer, 
increase  in  number  and  arrange  themselves  in  short  cylindrical  groups.  These 
are  the  first  traces  of  tubular  glands.  They  increase  in  length  and  extend 
downward  into  the  mesodermic  tissue.  For  a  time  the  cells  lining  the  peptic 
glands  are  all  apparently  alike,  but  at  about  the  fourth  month  the  differentia- 
tion into  chief  cells  and  parietal  cells  takes  place. 

In  the  intestines  a  proliferation  of  the  epithelium  and  of  the  underlying 


THE  DIGESTIVE  SYSTEM  297 

stroma  results  in  the  formation  of  villi.  These  appear  about  the  tenth  week, 
in  both  small  and  large  intestines.  In  the  former  they  increase  in  size,  while 
in  the  latter  they  atrophy  and  ultimately  disappear.  The  simple  tubular 
glands  of  the  intestines  develop  in  a  manner  similar  to  those  of  the  stomach. 

The  mesothelium  of  the  serosa  is  derived  from  the  mesodermic  cells  of  the 
primitive  body  cavity. 

The  development  of  the  larger  glands,  connected  with  the  digestive  tract, 
takes  place  in  a  manner  similar  to  the  formation  of  the  simple  tubular  glands. 
All  originate  in  extensions  downward  of  entodermic  cords  into  the  underlying 
mesodermic  tissue.  From  the  lower  ends  of  these  cords,  branches  extend  in 
all  directions  to  form  the  complex  systems  of  tubules  found  in  the  compound 
glands. 

The  salivary  glands  being  developed  from  the  oral  cavity,  originate  in  similar 
invaginations  of  ectodermic  tissue. 

The  pancreas  originates  as  three  separate  evaginations  from  the  entoderm  of 
the  future  duodenum.  Of  these,  one  atrophies,  while  the  other  two  unite  to 
develop  the  adult  pancreas.  The  two  evaginations  account  for  the  two 
pancreatic  ducts.  The  evaginations  take  place  into  the  underlying  mesenchyme, 
which  develops  the  connective-tissue  framework  of  the  organ.  The  growths  are 
at  first  solid  cords  of  cells  which  later  become  hollowed  out  to  form  tubules  and 
differentiate  chief  and  centro-acinar  cells,  the  former  early  showing  zymogen 
granules.  Increase  in  size  of  the  gland  is  accomplished  by  continuous  budding 
and  extension  of  tubules.  In  some  of  the  tubules  the  epithelial  cells  become 
darker  and  arranged  as  a  wall  around  a  mass  of  developing  blood  cells.  These 
structures  are  known  as  primary  islands.  Neither  their  function  nor  subsequent 
history  is  known.  Later  in  development  some  of  the  gland  tubules  lose  their 
lumina,  the  zymogen  granules  disappear  from  their  cells  and  the  whole  becomes 
transformed  into  a  secondary  island  or  island  of  Langerhans  of  the  adult  pancreas. 
According  to  Lageusse  a  transformation  of  islands  into  tubules  also  occurs,  and 
this  process  of  transformation  of  tubules  into  islands  and  islands  into  tubules 
persists  throughout  life.  Claude  on  the  other  hand  derives  both  primitive 
islands  and  islands  of  Langerhans  from  the  mesenchyme.  Recent  observations 
tend  to  support  the  former  of  these  views. 

The  liver  originates  as  a  downgrowth  of  the  entoderm  of  the  ventral  wall 
of  the  future  duodenum  into  the  mesoderm  of  the  transverse  septum.  At  its 
cephalic  end  the  downgrowth  is  solid  and  gives  rise  to  the  liver;  at  the  caudal 
end  it  is  hollow  and  gives  rise  to  the  gall-bladder.  As  the  evagination  increases 
in  size  it  becomes  almost  completely  separated  from  the  intestine,  the  slender 
connection  which  does  remain  becoming  the  ductus  cholcdochus.  Between  the 
latter  and  the  liver  anlage  a  slender  connection  also  remains,  the  cystic  duct. 
The  mesenchyme  surrounding  these  structures  develops  their  connective-tissue 
framework.  As  the  liver  outgrowths  develop  they  come  into  relation  with  the 
omphalomesenteric  veins  in  such  a  manner  that  the  vessels  are  broken  up  into 
an  anastomosing  network  of  smaller  vessels,  while  the  liver  cells  dcvelof)  into 
anastomosing  hepatic  cylinders.  These  resemble  the  tubules  of  other  glands 
in  that  the  walls  are  formed  by  many  cells.  The  manner  in  which  these  are  trans- 
formed into  the  slender  hepatic  cords  of   the  adult  liver  is  not  known.     The 


298  THE  ORGANS 

change  begins  to  take  place  about  the  time  of  birth  in  man.  The  breaking  up 
of  the  larger  vessels  into  smaller  by  ingrowth  of  the  cords  of  liver  cells  gives 
rise  to  the  so-called  sinusoidal  circulation. 

General  References  for  Further  Study 

Oppel:  Lehrbuch  der  vergleichenden  mikroskopischen  Anatomie. 

KoUiker:  Handbuch  der  Gewebelehre  des  Menschen. 

Opie:  The  Pancreas. 

Stohr:  Salivary  Glands,  in  Text-book  of  Histology. 


CHAPTER  VII 

THE  RESPIRATORY  SYSTEM 

The  respiratory  apparatus  consists  of  a  system  of  passages — nares, 
larynx,  trachea,  and  bronchi,  which  serve  for  the  transmission  of  air 
to  and  from  the  essential  organ  of  respiration,  the  lungs. 

The  Nares 

The  nares.  or  nasal  passages,  are  divided  into  vestibular,  respira- 
tory, and  olfactory  regions,  the  differentiation  depending  mainly  upon 
the  structure  of  their  mucous  membranes. 

The  VESTIBULAR  REGION  marks  the  transition  between  skin  and 
mucous  membrane  (page  220).  Its  epithehum  is  of  the  stratified 
squamous  variety  and  rests  upon  a  basement  membrane,  which  is 
thrown  into  folds  by  papillae  of  the  underlying  stroma.  The  latter  is 
richly  cellular,  and  contains  sebaceous  glands  (page  391)  and  the  fol- 
licles of  the  nasal  hairs. 

The  RESPIRATORY  REGION  is  much  larger  than  both  the  vestibular 
and  olfactory  regions.  Its  epithelium  is  of  the  stratified  columnar 
variety.  The  cells  of  the  surface  layer  are  ciliated  and  are  inter- 
spersed with  goblet  cells.  The  stroma  is  distinguished  by  its  thick- 
ness (3  to  5  mm.  over  the  inferior  turbinates)  and  by  the  presence  of 
networks  of  such  large  veins  that  the  tissue  closely  resembles  erectile 
tissue.  It  contains  considerable  diffuse  lymphoid  tissue  and  here  and 
there  small  lymph  nodules.  In  the  stroma  are  small  simple  tubular 
glands  lined  with  both  serous  and  mucous  cells.  There  is  no  sub- 
mucosa,  the  stroma  being  connected  directly  with  the  periosteum  and 
perichondrium  of  the  nasal  bones  and  cartilages. 

The  mucous  membrane  of  the  accessory  nasal  sinuses  is  similar  in 
structure  to  that  of  the  respiratory  region  of  the  nares,  Init  is  Ihimur 
and  contains  fewer  glands. 

The  (OLFACTORY  REGION  Can  be  distinguished  with  the  naked  eye 
by  its  brownish-yellow  color,  in  contrast  with  the  reddi.sh  tint  of  the 
surrounding  respiratory  mucosa.     The  ej)itli("liiini  is  of  the  stratilK-d 

2H\) 


300  THE  ORGANS 

columnar  type,  and  is  considerably  thicker  than  that  of  the  respira- 
tory region.  The  surface  cells  are  of  two  kinds:  (i)  sus tentacular 
cells,  and  (2)  olfactory  cells. 

(i)  The  sustentacular  cells  are  the  more  numerous.  Each  cell 
consists  of  three  parts:  {a)  A  superficial  portion,  which  is  broad  and 
cylindrical,  and  contains  pigment,  and  granules  arranged  in  longi- 
tudinal rows.  The  cells  have  well-marked,  striated,  thickened  free 
borders,  which  unite  to  form  the  so-called  membrana  limitans  olfactoria. 
(b)  A  middle  portion  which  contains  an  oval  nucleus.  As  the  nuclei 
of  these  cells  all  he  in  the  same  plane,  they  form  a  distinct  narrow 
band,  which  is  known  as  the  zone  of  oval  nuclei,  (c)  A  thin  filament- 
ous process  which  extends  from  the  nuclear  portion  down  between  the 
cells  of  the  deeper  layers.  This  process  is  irregular  and  pitted  by 
pressure  of  surrounding  cells.  It  usually  forks  and  apparently 
anastomoses  with  processes  of  other  cells  to  form  a  sort  of  proto- 
plasmic reticulum. 

(2)  The  olfactory  cells  Ue  between  the  sustentacular  cells.  Their 
nuclei  are  spherical,  lie  at  different  levels,  and  are  most  of  them  more 
deeply  placed  than  those  of  the  sustentacular  cells.  They  thus  form 
a  broad  band,  the  zone  of  round  nuclei.  From  the  nuclear  portion  of 
the  cell  a  delicate  process  extends  to  the  surface,  where  it  ends  in  sev- 
eral minute  hair-Hke  processes.  From  the  opposite  pole  of  the  cell  a 
longer  process  extends  centrally  as  a  centripetal  nerve  fibre.  The 
olfactory  cell  is  thus  seen  to  be  of  the  nature  of  a  ganglion  cell  (see 
also  page  426). 

Between  the  nuclear  parts  of  the  olfactory  cells  and  the  basement 
membrane  are  the  basal  cells.  These  are  small  nucleated  elements, 
the  irregular  branching  protoplasm  of  which  anastomoses  with  that 
of  neighboring  basal  cells  and  of  the  sustentacular  cells  to  form  the 
peculiar  protoplasmic  reticulum  already  mentioned. 

The  basement  membrane  is  not  well  developed. 

The  stroma  consists  of  loosely  arranged  white  fibres,  delicate  elastic 
fibres,  and  connective-tissue  cells.  Embedded  in  the  stroma  are 
large  numbers  of  simple  branched  tubular  glands,  the  glands  of  Bow- 
man. Each  tubule  consists  of  a  duct,  a  body,  and  a  fundus.  The 
secreting  cells  are  large  and  irregular  and  contain  a  yellowish  pigment, 
which  with  that  of  the  sustentacular  cells  is  responsible  for  the  peculiar 
color  of  the  olfactory  mucosa.  These  glands  were  long  described  as 
serous,  but  are  now  believed  to  be  mucous  in  character.  They  fre- 
quently extend  beyond  the  limits  of  the  olfactory  region. 


THE  RESPIRATORY  SYSTEM  301 

The  Larynx 

The  larynx  consists  essentially  of  a  group  of  cartilages  united  by 
strong  fibrous  bands  and  Hned  by  mucous  membrane. 

The  epithelium  covering  the  true  vocal  cords,  the  laryngeal  sur- 
face of  the  epiglottis,  and  the  anterior  surface  of  the  arytenoid  carti- 
lages is  of  the  stratified  squamous  variety  with  underlying  papillas. 
With  these  exceptions  the  mucous  membrane  of  the  larynx  is  lined 
\\'ith  stratified  columnar  ciHated  epitheHum  similar  to  that  of  the  re- 
spiratory portion  of  the  nares.  Numerous  goblet  cells  are  usually 
present,  and  the  epithehum  rests  upon  a  broad  basement  membrane. 
On  the  posterior  surface  of  the  epiglottis  many  taste  buds  (see  Fig.  297 
and  page  587)  are  embedded  in  the  epithehum. 

The  stroma  is  especially  rich  in  elastic  fibres.  The  true  vocal 
cords  consist  almost  wholly  of  longitudinal  elastic  fibres  covered  by 
stratified  squamous  epithehum.  Lymphoid  cells  are  present  in  vary- 
ing numbers.  In  some  places  they  are  so  numerous  that  the  tissue 
assumes  the  character  of  diffuse  lymphoid  tissue.  Distinct  nodules 
sometimes  occur. 

Owing  to  the  absence  of  a  muscularis  mucosae  the  stroma  passes 
over  with  no  distinct  fine  of  demarcation  into  the  submucosa.  This 
is  a  more  loosely  arranged,  less  cellular  connective  tissue,  and  con- 
tains simple  tubular  glands  Hned  with  both  serous  and  mucous  cells. 

Externally  the  submucosa  merges  into  a  layer  of  more  dense 
fibrous  tissue  which  connects  it  with  the  laryngeal  cartilages  and 
with  the  surrounding  structures.  Immediately  surrounding  the 
cartilages  the  connective  tissue  forms  an  extremely  dense  layer,  the 
perichondrium. 

Of  the  cartilages  of  the  larynx,  the  epiglottis,  the  middle  part  of 
the  thyreoid,  the  apex  and  vocal  process  of  the  arytenoid,  the  carti- 
lages of  Santorini  and  of  Wrisburg  are  of  the  yellow  elastic  variety. 
The  main  body  of  the  arytenoid,  the  rest  of  the  thyreoid  and  the  cri- 
coid cartilages  are  hyaline.  After  the  twentieth  year,  more  or  less 
ossification  is  usually  found  in  the  cricoid  and  thyreoid  cartilages. 

The  Trachea 

The  walls  of  the  trachea  consist  of  three  layers — mucosa,  submu- 
cosa, anrl  fil^rosa  (Fig.   199). 

The  mucosa  is  continuous  with  that  of  the  larynx,  which  it  closely 
resembles  in  structure.     It  consists  of  a  stratified  columnar  ciliated 


302 


THE  ORGANS 


epithelium,  with  numerous  goblet  cells,  resting  upon  a  broad  base- 
ment membrane,  and  of  a  stroma  of  mixed  fibrous  and  elastic  tissue 
containing  many  lymphoid  cells. 

The  submucosa  is  not  distinctly  marked  off  from  the  stroma  on 
account  of  the  absence  of  a  muscularis  mucosae.  It  is  distinguished 
from  the  stroma  by  its  looser,  less  cellular  structure,  by  its  numerous 
large  blood-vessels,  and  by  the  presence  of  glands.  These  are  of  the 
simple  branched  tubular  variety  and  are  lined  with  both  serous  and 


'■U'.iii^iiuUMaUiiJ±JtV,,,':-.\-.::'.-.i  ii^g~ 


'^'.^/••^'t; 


-  h 


--d 


Fig.  199. — From  Longitudinal  Section  of  Human  Trachea.  X40.  (Technic  3,  p 
304.)  a,  Epithelium;  b,  stroma;  c,  cartilage;  d,  fibrous  coat;  e,  serous  tubules;/,  mucous 
tubules;  g,  glands  in  submucosa;  h,  ducts. 

mucous  cells.  Some  of  the  mucous  tubules  have  well-marked  cres- 
cents of  Gianuzzi.  The  glands  are  most  numerous  between  the  ends 
of  the  cartilaginous  rings,  where  they  frequently  penetrate  the  muscle 
and  extend  into  the  fibrosa. 

The  fibrosa  is  composed  of  coarse,  rather  loosely  woven  connect- 
ive-tissue fibres  embedded  in  which  are  the  tracheal  cartilages.  These 
are  incomplete  rings  of  hyahne  cartilage  shaped  Hke  the  letter  C 
(Fig.  200).  They  are  from  sixteen  to  twenty  in  number  and  encircle 
about  four-fifths  of  the  tube,  being  open  posteriorly.     The  openings 


THE  RESPIRATORY  SYSTEM 


303 


between  the  ends  of  the  cartilaginous  rings  are  bridged  over  by  a 
thickened  continuation  of  the  fibrous  coat,  strengthened  by  a  layer 
of  smooth  muscle  (Fig.  200,  m).  The  bundles  of  muscle  cells  run 
mainly  in  a  transverse  direction,  and  extend  across  the  intervals 
between  adjacent  rings  as  well  as  between  their  open  ends.     There 


^■ 


'^ 


YiG.  200. — Transverse  Section  of  Human  Trachea  through  One  of  the  Cartilage 
Rings.  X8.  (KoUiker.)  E,  EpithcHum  of  {s)  mucous  membrane;  dr,  glancls;  us, 
gland  duct;  ad,  adenoid  tissue;  A',  cartilage;  m,  smooth  muscle  cut  longitudinally, 
extending  across  between  ends  of  cartilage  ring. 

are  frequently  a  few  bundles  of  obliquely  disposed  cells  and,  most 
external,  some  few  that  run  longitudinally. 

Outside  the  fibrous  coat  proper  is  a  looser,  more  irregular  con- 
nective tissue,  which  serves  to  attach  the  trachea  to  the  surrounding 
structures. 

Blood-vessels,  lymphatics,  and  nerves  have  a  similar  distribution 
in  larynx  and  trachea.  The  larger  vessels  pass  directly  to  the  sub- 
muc(jsa.  From  these,  smaller  branches  pass  to  the;  different  coats, 
where  they  break  up  into  capillary  networks. 


304  THE  ORGANS 

Lymphatics  form  plexuses  in  the  submucosa  and  mucosa,  the 
most  superficial  lying  just  beneath  the  subepithelial  capillary  plexus. 

The  nerves  of  the  larynx  and  trachea  are  derived  from  both  cere- 
bro-spinal  and  sympathetic  systems.  The  cerebro-spinal  nerves  are 
afferent,  the  dendrites  of  spinal  ganghon  cells.  They  form  a  sub- 
epithehal  plexus  from  which  are  given  off  fibrils  which  pass  into  the 
epithelium  and  terminate  freely  among  the  epithelial  cells.  Other 
afferent  fibres  of  cerebro-spinal  nerves  pass  to  the  muscular  coat  of 
the  trachea.  Sympathetic  nerve  fibres  form  plexuses  which  are  inter- 
spersed with  minute  groups  of  ganglion  cells.  Axones  from  these 
ganghon  cells  have  been  traced  to  the  smooth  muscle  cells  of  the 
trachea.  Sympathetic  axones  also  pass  to  the  glands  of  the  trachea 
and  larynx.  On  the  under  surface  of  the  epiglottis  small  taste  buds 
are  found. 

TECHNIC 

(i)  For  the  study  of  the  details  of  structure  of  the  walls  of  the  nares  and 
larynx,  fix  small  pieces  of  perfectly  fresh  material  from  different  regions  in 
formalin-Miiller's  fluid  (technic  5,  p.  7),  harden  in  alcohol,  stain  sections  with 
haematoxylin-eosin  (technic  i,  p.  20),  and  mount  in  balsam. 

(2)  The  general  relations  of  the  parts  can  be  studied  by  removing  the  larynx, 
upper  part  of  the  trachea,  and  corresponding  portion  of  the  oesophagus  of  an 
animal  or  of  a  new-born  child,  fixing  and  hardening  as  above,  and  cutting  longi- 
tudinal sections  through  the  entire  specimen. 

(3)  Trachea. — Remove  a  portion  of  the  trachea  and  treat  as  in  technic  (i). 
Both  longitudinal  and  transverse  sections  should  be  made;  the  longitudinal  in- 
cluding at  least  two  of  the  cartilaginous  rings;  the  transverse  being  through  one 
of  the  rings. 

The  Bronchi 

The  primary  bronchi  and  their  largest  branches  have  essentially 
the  same  structure  as  the  trachea  except  that  the  cartilaginous  rings 
are  not  as  complete.  Bronchi  branch  at  acute  angles  and  also  give 
off  small  side  branches. 

As  they  decrease  in  caHbre,  the  following  changes  take  place  in 
their  walls  (Figs.  201  to  204). 

(i)  The  epitheUum  gradually  becomes  thinner.  In  a  bronchus 
of  medium  size  (Fig.  201)  it  has  become  reduced  to  three  layers  of 
cells,  which  Kolhker  describes  as  an  outer  "basal"  layer,  a  middle 
"replacing"  layer,  and  a  surface  layer  of  ciliated  and  goblet  cells. 
In  the  smaller  bronchi  (Figs.  203,  204)  the  epithelium  is  reduced  to  a 


THE  RESPIRATORY  SYSTEM 


305 


single  layer  of  ciliated  cells.  These  are  at  first  high,  but  become 
gradually  lower  as  the  bronchi  become  smaller,  until  in  the  terminal 
branches  the  epithelium  is  simple  cuboidal  and  non-cihated.  Among 
the  cihated  cells  are  varying  numbers  of  mucous  or  goblet  cells. 

(2)  The  stroma  decreases  in  thickness  as  the  bronchi  become 
smaller.  It  consists  of  loosely  arranged  white  and  elastic  fibres. 
This  layer  with  the  epithehum  is  folded  longitudinally  (Fig.  204). 
There  is  considerable  diffuse  lymphatic  tissue,  and  in  some  places 
small  nodules  occur,  over  which  there  may  be  lymphoid  infiltration 


Fig.  201. — Transverse  Section  through  two  Medium-size  Bronchi  of  the  Human 
Lung.  X  15.  (Technic  2,  p.  317)  In  the  fibrous  coat  are  seen  the  bronchial  arteries 
and  veins,  a,  Epithelium;  b,  stroma;  c,  muscularis  mucosae;  d,  lung  tissue;  e,  fibrous 
coat;  /,  plates  of  cartilage. 


of  the  epithelium  (see  Tonsil,  page  179).  Near  the  root  of  the  lung 
many  small  lymph  nodules  are  found,  which  show  different  degrees  of 
pigmentation. 

(3)  With  decrease  in  thickness  of  the  epithelium  and  of  the 
stroma,  the  thickness  of  the  mucosa  is  maintained  by  the  appearance 
of  a  layer  of  smooth  muscle.  In  the  larger  bronchi  this  is  a  contin- 
uous layer  of  circularly  disposed  smooth  muscle,  and  lies  just  external 
to  the  stroma,  forming  a  muscularis  mucosa?  (Fig.  202) .  It  reaches  its 
greatest  thickness  relative  to  the  size  of  the  bronchus  in  the  bronchi 
of  medium  size.  As  the  bronchi  become  smaller  it  becomqs  thinner, 
then  discontinuous,  and  in  the  smallest  bronchi  consists  of  only  a 
few  scattered  muscle  cells.  These  continue  into  the  walls  of  the 
alveolar  ducts,  but  are  absent  beyond  this  j)oint. 

(4)  The  submucosa  decreases  in  thickness  with  decrease  in  the 


306 


THE  ORGANS 


calibre  of  the  bronchi.  It  consists  of  loosely  arranged  connective 
tissue.  Mixed  glands  (Fig.  202)  are  present  until  a  diam.eter  of  about . 
I  mm.  is  reached,  when  they  disappear.  They  lie  in  the  submucosa 
and  frequently  extend  through  between  the  cartilage  plates  into  the 
fibrous  coat.  The  ducts  pass  through  the  muscular  coat  and  open 
into  pit-Hke  depressions  lined  with  a  continuation  of  the  surface 
ciliated  epithelium. 

(5)  The  cartilages,  which  in  the  trachea  and  primary  bronchi 
form  nearly  complete  rings,  become  gradually  smaller,  and  finally 
break  up  into  short  disconnected  plates  (Figs.  201  and  202).     They 


Muscle 
Epithelium        Stroma        coat 


Alveol 


Nerve 

Blood-vessel 
Fat 


Cartilage  ^         \    \  >/-A\    f 


Excretory  duct 


Fig.  202. — Cross  Section  of  Human  Bronchus  (of  a  child)  of  2  mm.  diameter.     X30. 

(Stohr.) 


are  frequently  fibrocartilage  rather  than  hyaline.  These  plates  de- 
crease in  size  and  number,  and  are  absent  after  a  diameter  of  i  mm. 
is  reached.  Cartilage  and  mucous  glands  thus  disappear  at  about  the 
same  time,  although  it  is  common  for  glands  to  extend  over  into 
smaller  bronchi  than  do  the  cartilage  plates. 

The  bronchi  down  to  a  diameter  of  from  1.5  to  i  mm.  are  inter- 
lobular, and  belong  to  the  duct  system  down  to  a  diameter  of  about 


THE  RESPIRATORY  SYSTEM 


307 


0.5  mm.  From  the  small  interlobular  bronclii  are  given  off  the  ter- 
minal bronchi.  These  are  respiratory  in  character  and  are  described 
with  the  lungs. 


Fig.  203. — Transverse  Section  of  Small  Bronchus  from  Human  Lun^.      XiiS-     (Tech- 
nic  2,  p.  317.)     a,  Stroma;  b,  epithelium;  c,  muscularis  mucosa;;  d,  fibrous  coat. 


:s 


^ 


Fig.  204. — Transverse  Section  throuj^h  small  lirom  hus  of  Human  i>unK.  (Sobotta.) 
Simple  columnar  ciliated  eijithelium  ;  no  cartilage;  no  Khm''^;  mucosa  folded  longitudi- 
nally; elastic  tissue  stained  with  W'eigert's  elastic  tissue  stain. 

In  studying  the  bronchi  it  is  convenient  to  arbitrarily  divide  ihcm  into  large, 
medium-sized,  and  small  bronchi. 

Lar^e  bronchi  have  essentially  the  same  structure  as  llie  trachea  except  for 
somewhat  thinner  walls. 

Medium-sized  bronchi  (P"ig.  201)  have  an  ejiiilH  lium  aixjut  three  layers  deep, 
disconnected  plates  of  cartilage,  a  continuous  iayir  of  sinootli  iiuiscle  disposed 
circularly  as  a  muscularis  mucosx-  and  tubular  glands. 


308  THE  ORGANS 

Small  bronchi  have  a  single  layer  of  ciliated  epithelium,  a  thinner  muscular 
coat,  no  glands,  and  no  cartilage.     (Figs.  203,  204.) 

The  Lungs 

The  lung  is  built  upon  the  plan  of  a  compound  alveolar  gland,  the 
trachea  and  bronchial  ramifications  corresponding  to  duct  systems, 
the  air  vesicles  to  gland  alveoli. 

The  surface  of  the  lung  is  covered  by  a  serous  membrane — the 
pulmonary  pleura — which  forms  its  capsule,  and  which  at  the  root 
of  the  lung,  or  hilum,  is  reflected  upon  the  inner  surface  of  the  chest 


Fig.  205. — From  Lung  of  an  Ape.  The  bronchi  and  their  dependent  ducts  and 
alveoli  have  been  fiUed  with  quicksilver.  X15.  (KoUiker,  after  Schulze.)  Z>,  Terminal 
bronchus;  a,  alveolar  duct;  i,  alveoli. 

wall  as  the  parietal  pleura.  It  consists  of  fibrillar  connective  tissue 
containing  fine  elastic  fibres  which  are  more  numerous  in  the  visceral 
than  in  the  parietal  layer.  From  the  capsule  broad  connective- 
tissue  septa  pass  into  the  organ,  dividing  it  into  lobes.  From  the 
capsule  and  interlobar  septa  are  given  off  smaller  septa,  which  sub- 
divide the  lobes  into  lobules. 

The  human  pulmonary  lobule  (Figs.  206  and  208)  is  the  anatomic 
unit  of  lung  structure.  Each  lobule  is  complete  in  itself,  having  its 
own  bronchial  system,  its  own  vascular  system,  and  being  more  or 
less  completely  separated  from  its  neighbors  by  connective  tissue. 
In  the  young  and  in  some  lower  animals  the  lobule  is  quite  plainly 
outlined  by  connective  tissue,  but  in  the  human  adult  the  amount 
of  connective  tissue  is  extremely  small,  and  the  lobules,  especially  the 
more  central,  difficult  of  definition.  The  lobules  are  best  observed 
at  the  surface  of  the  lung  where  their  bases  which  lie  against  the  pleura 
can  be  seen  with  the  naked  eye.     This  is  especially  true  in  the  aged 


THE  RESPIRATORY  SYSTEM 


309 


where  carbon  deposits  in  the  interlobular  connective  tissue  assist  in 
outhning  the  lobules.  Thebase  of  the  peripheral  lobule  is  four-  toeight- 
sided  and  from  i  to  1.5  cm.  in  diameter.  It  is  pyramidal  in  shape, 
narrowing  to  an  apex  about  i  to  1.5  cm.  from  the  base.  In  the  inte- 
rior of  the  lung  the  lobules  are  not  pyramidal  but  irregularly  poly- 
hedral, the  apex  being,  however,  distinguishable  by  the  entrance  of 
the  lobular  bronchus. 

The  apex  of  each  lobule  is  the  point  of  entrance  of  the  lobular 
bronchus  (branch  of  inter-  or  sublobular)  (Figs.  205,  and  208,  hi) 
which  is  about  0.5  mm.  in  diameter,  and  of  the  lobular  branch  of  the 


Bronchial  artery 


Pumonary  vein 


Pulmonary  artery 


"Terminal  bronchus 


T. ■  Alveolar  passage 


Pleural  capillaries 


Fig.  206. — Scheme  of  a  Pulmonary  Lobule  and  its  Blood  Sui)ply.  (Stohr.)  The 
two  main  branches  of  the  pulmonary  vein  are  seen  lying  in  the  interlobular  connective 
tissue. 

pulmonary  artery.  Accompanied  by  the  artery  (Fig.  206)  the  bron- 
chus passes  through  the  central  axis  of  the  lobule,  giving  off  collateral 
branches  (Fig.  205,  a,  b),  to  about  the  middle  of  the  lobule,  where  it 
divides  into  two  branches  (Fig.  206).  These  branches  and  also  the 
collaterals  branch  dichotgrnously  giving  rise  to  from  50  to  100  ter- 
minal or  alveolar  bronchi  ("terminal",  as  being  the  last  subdivision 
of  the  bronchial  tree  which  preserves  its  identity  as  a  bronchus; 
"alveolar",  as  it  gives  off  especially  toward  its  distal  end,  some 
alveoli).     From  each  terminal  bronchus  open  from  three  to  six  narrow 


310 


THE  ORGANS 


passages^alveolar  passages  or  alveolar  ducts — from  which  are  given 
off  the  alveoli — air  vesicles  or  air  cells.  The  somewhat  dilated  distal 
end  of  the  alveolar  passage  is  sometimes  designated  the  alveolar  sac 
or  infundibulum.  Laguesse  divides  the  lobule  schematically  into 
three  parts  a  proximal  part  containing  the  intralobular  bronchus 
and  collaterals,  a  middle  part  in  which  the  main  division  of    the 


Alveolar  sacs 


Blood-vessel 


Respiratory  bronchus 


Alveoli 


Small  bronchus 


Fig.  207. — ^Section  of  Cat's  Lung  (Szymonowicz),  surface  lobule;  respiratory  bronchus 
opening  into  alveolar  duct  from  which  are  given  off  two  alveolar  sacs. 


lobular  bronchus  occurs,  and  a  third  part  containing  the  alveolar 
bronchi  and  alveoH. 

The  terminal  bronchus.  The  proximal  portion  of  the  terminal 
bronchus  is  lined  by  a  simple  columnar  ciliated  epithelium,  resting 
upon  a  basement  membrane.  Beneath  this  is  a  richly  elastic  stroma 
containing  bundles  of  circularly  disposed  smooth  muscle  cells. 
The  epitheUum  becomes  gradually  lower  and  non-ciliated,  and  near 


THE  RESPIRATORY  SYSTEM 


311 


the  distal  end  of  the  terminal  bronchus  there  appear  small  groups  or 
islands  of  flat,  non-nucleated  epithelial  cells — respiratory  epithelium 
f^The  alveolar  passage.     Here  the  cuboidal  epithelium  is  almost 
completely  replaced  by  the  respiratory.     Beneath  the  epithelium  the 
walls  have  a  structure  similar  to  those  of  the  distal  end  of  the  terminal 


u 


§ 


-^6.  A 


r 


"^Ji-c' 


./•'^ 


I 


-4<  r 


-"X^r?" 


Fig.  208. — Section  of  Lung  of  Rat  to  show  Arrangement  of  Bronchial  Ramifications  and 
of  Alveoli  within  a  Single  Lobule.  W,  Lobular  or  sublobular  bronchus;  6i/,  intralobular 
bronchus;  ba,  terminal  bronchus;  v,  dilatation  sometimes  called  vestibule;  ca,  alveolar 
canal;  i,  portion  sometimes  called  infundibulum;  d,  alveoli,  some  of  which  are  so  cut  as  to 
show  their  openings  into  the  infundibulum  and  alveolar  canals,  etc.,  while  others  api)ear 
closed.     X60.     (Prenant.; 

bronchus,  consisting  of  delicate  libro-clastic  tissue  with  scattered 
smooth  muscle  cells.     The  basement  membrane  is  extremely  thin. 

The  alveolus.  The  epithelium  of  the  alveolus  consists  of  two  kinds 
of  cells,  respiratory  cells  and  so-called  "fcBlal"  cells  (see  Develop- 
ment, page  3 1 5 j. 

The  respiratory  cells  (Fig.  209)  are  some  of  ihcni  large,  Hat,  non- 
nucleated  j)lates,  while  others  are  much  smaller,  non-nucleated  ele- 


312 


THE  ORGANS 


ments.  The  absence  of  nuclei  and  the  extremely  small  amount  of 
intercellular  substance  render  these  cells  quite  invisible  in  sections 
stained  by  the  more  common  methods.  The  cell  boundaries  are  best 
demonstrated  by  means  of  silver  nitrate  (technic  i,  p.  78). 

The  "fcetar'  cells  are  granular,  nucleated  cells  which  are  scattered 
among  the  respiratory  cells.  Their  position  appears  to  be  less  super- 
ficial than  that  of  the  respiratory  cells,  the  foetal  cells  lying  in  the 
meshes  of  the  capillary  network,  the  respiratory  cells  covering  the 
capillaries.     In  the  embryonic  lung  and  in  the  lungs  of  a  still-born 


Fig.  209, — ^From  Section  of  Cat's  Lung  Stained  with  Silver  Nitrate.  (Klein.) 
(Technic  i,  p.  78.)  Small  bronchus  surrounded  by  alveoli,  in  which  are  seen  both  flat 
cells  (respiratory  epithelium)  and  cuboidal  cells  (foetal  cells). 


child  the  air  passages  and  alveoli  contain  only  this  type  of  cells,  the 
small  flat  plates  apparently  resulting  from  a  flattening  out  of  the 
cuboidal  cells  due  to  pressure  from  inspiration,  and  the  large  flat 
plates  to  union  of  a  number  of  small  plates.  Delicate  elastic  fibrils 
support  the  respiratory  and  foetal  cells.  Around  the  opening  of  the 
alveolus  the  elastic  fibres  are  more  numerous,  forming  a  more  or 
less  definite  ring.  The  disposition  of  elastic  tissue  in  the  wall  of  the 
alveoli  is  undoubtedly  of  importance  in  determining  the  contraction 
and  expansion  of  the  alveoli  under  varying  conditions  of  pressure.  It 
has  been  estimated  that  on  forced  inspiration  an  alveolus  can  expand 
to  three  times  its  resting  capacity.  Each  alveolus  communicates 
not  only  with  its  alveolar  passage,  or  alveolar  bronchus,  by  means  of  a 


THE  RESPIRATORY  SYSTEM 


313 


broad    opening,    but    alveoli    are  connected  with  one  another  by 
minute  openings  in  their  walls. 

The  interalvcolar  connective  tissue,  while  extremely  small  in  amount, 
serves  to  separate  the  alveoli  from  one  another.  Somewhat  thicker 
connective  tissue  separates  the  alveoli  of  one  alveolar  passage  from 
those  of  another.  Still  stronger  connective-tissue  bands  as  already 
noted  separate  adjacent  lobules. 


Fig.  2IC. — Section  Through  Three  Alveoli  of  Human  Lung._  X235.  Weigert's 
elastic-tissue  stain  (technic  3,  p.  28)  to  show  arrangement  of  elastic  tissue,  a,  Alveolus 
cut  through  side  walls  only;  b,  alveolus  cut  through  side  walls  and  portion  of  bottom  or 
top;  c,  alveolus  in  which  either  the  bottom  or  top  is  included  in  section. 

Blood-vessels. — Two  systems  of  vessels  distribute  blood  to  the 
lungs.  One,  the  bronchial  system,  carries  blood  for  the  nutrition  of 
the  lung  tissue.  The  other,  the  much  larger  pulmonary  system, 
carries  blood  for  the  respiratory  function  (Fig.  206). 

The  bronchial  artery  and  the  pulmonary  artery  enter  the  lung  at  its 
hilum.  Within  the  lung  the  vessels  branch,  following  the  branchings 
of  the  bronchi,  which  they  accompany  (Fig.  206).  The  pulmonary 
vessels  are  much  the  larger  and  run  in  the  connective  tissue  outside 
the  bronchial  walls.  The  bronchial  vessels  lie  within  the  fibrous 
coat  of  the  bronchus.  A  section  of  a  bronchus  thus  usually  shows 
the  large  pulmonary  vessels,  one  on  either  side  of  the  bronchus,  and 
two  or  more  small  bronchial  vessels  in  the  walls  of  the  bronchus 
(Fig.  201). 

The  pulmonary  lobule  forms  a  distinct  "blood-vascular  unit."  A 
branch  of  the  pulmonary  artery  enters  the  apex  of  each  lobule  close 


314  THE  ORGANS 

to  the  lobular  bronchus,  and  almost  immediately  breaks  up  into 
branches,  one  of  which  passes  to  each  alveolar  passage  (Fig.  206). 
From  these  are  given  off  minute  terminal  arterioles  which  pass  to  the 
central  sides  of  the  alveolar  passages  and  alveoli,  where  they  give 
rise  to  a  rich  capillary  network.  This  capillary  network  is  extremely 
close-meshed,  and  invests  the  alveoli  on  all  sides  (Fig.  211).  Similar 
networks  invest  the  walls  of  the  respiratory  bronchi,  the  alveolar 
ducts,  and  their j.  alveoli.  All  of  these  capillary  networks  freely 
anastomose. 


--^ 


Fig.  211. — Parts  of  Four  Alveoli  from  Section  of  Injected  Human  Lung.  X200. 
(Technic  5,  p.  317.)  a,  Wall  of  alveolus  seen  on  flat;  c,  same,  but  only  small  part  of 
alveolar  wall  in  plane  of  section;  b,  alveoli  in  which  plane  of  section  includes  only  side 
walls;  alveolar  wall  seen  on  edge. 

There  are  thus  interposed  between  the  blood  in  the  capillaries 
and  the  air  in  the  alveoli  only  three  extremely  thin  layers:  (i)  The 
thin  endothelium  of  the  capillary  wall;  (2)  the  single  layer  of  flat 
respiratory  epithelial  plates;  and  (3)  the  delicate  basement  membrane 
upon  which  the  respiratory  epithelium  rests  together  with  an  extremely 
small  amount  of  fibrous  and  elastic  tissues  (see  diagram,  Fig.  212.) 

The  veins  begin  as  small  radicles,  one  from  the  base  of  each  alve- 
olus (Fig.  206).  These  empty  into  small  veins  at  the  periphery  of  the 
lobule.     These  veins  at  first  run  in  the  interlobular  connective  tissue 


THE  RESPIRATORY  SYSTEM  315 

away  from  the  artery  and  bronchus.     Later  they  empty  into  the 
large  pulmonary  trunks  which  accompany  the  bronchi. 

The  bronchial  arteries  break  up  into  capillary  networks  in  the  walls 
of  the  bronchi,  supplying  them  as  far  as  their  respiratory  divisions, 
beyond  which  point  the  capillaries  belong  to  the  pulmonary  system. 
The  bronchial  arteries  supply  the  walls  of  the  bronchi,  the  bronchial 
lymph  nodes,  the  walls  of  the  pulmonary  vessels,  and  the  pulmonary 
pleura.  Of  the  bronchial  capillaries  some  empty  into  the  bronchial 
veins,  others  into  the  pulmonary  veins. 

Air  y'-   a 


Blood  ""•-  C 

Fig.  212. — Diagram  of  Tissues  Interposed  Between  Blood  and  Air  in  Alveolus,  a, 
Respirator}-  epithelium;  b,  fibro-elastic  tissue;  c,  endothelium  of  capillary.  As  h  does 
not  form  a  continuous  membrane,  the  capillary  wall  is  in  many  places  in  direct  apposi- 
tion with  the  respiratory  epithelium,  so  that  only  two  layers,  a  and  b,  are  interposed 
between  blood  and  air. 

Lymphatics.— The  lymphatics  of  the  lung  begin  as  small  lymph 
spaces  in  the  interalveolar  connective  tissue.  These  communicate 
with  larger  lymph  channels  in  the  interlobular  septa.  Some  of  these 
empty  into  the  deep  pulmonary  lymphatics,  which  follow  the  pul- 
monary vessels  to  the  lymph  glands  at  the  root  of  the  lung.  Others 
empty  into  the  superficial  pulmonary  lymphatics,  which  form  an 
extensive  subpleural  plexus  connected  with  small  subpleural  lymph 
nodes,  whence  by  means  of  several  larger  vessels  the  lymph  is 
carried  to  the  lymph  nodes  at  the  hilum. 

Nerves. — Bundles  of  medullated  and  non-meduUated  fibres  accom- 
pany the  bronchial  arteries  and  veins.  Small  sympathetic  ganglia 
are  distributed  along  these  nerves.  The  fibres  form  plexuses  in  the 
fibrous  layer  of  the  bronchi,  from  which  terminals  pass  to  the  muscle 
of  the  bronchi  and  of  the  vessel  walls  and  to  the  mucosa.  Free  end- 
ings upon  the  epithelium  of  bronchi,  air  passages,  and  alveoli  have 
been  described. 

Development  or  the  Respir.'Vtory  System 

The  epithelium  of  the  respiratory  system  develops  from  entoderm,  the  con- 
nective-tissue elements  from  mesoderm.  The  first  differentiation  of  respiratory 
system  appears  as  a  dipping  down  of  the  entoderm  of  the  floor  of  the  primitive 
pharynx  (some  investigators  describe  two  original  evaginations,  one  for  each 
lung).  The  tubule  thus  formed  divides  into  a  larger  and  longer  right  branch, 
which  subdivides  into  three  branches  corresponding  to  the  three  lobes  of  the 
future  right  lung,  (Fig.  213,  b,  b,  b)  and  a  smaller  and  shorter  left  branch,  which 
subdivides  into  two  branches  corresponding  to  the  two  lobes  of  the  future  left 


316 


THE  ORGANS 


lung.  By  repeated  subdivisions  of  these  tubules  the  entire  bronchial  system  is 
formed.  Up  to  this  point  (about  six  months  in  human  foetus)  the  development 
is  that  of  a  compound  alveolar  gland,  (Fig.  213).  The  last  to  develop  are  the 
respiratory  divisions  of  the  bronchi  with  their  alveolar  passages  and  alveoli. 
The  appearance  of  the  alveoli  is  wholly  characteristic  of  lung  (Fig.  213,  vpd.) 
The  epithelium  of  the  alveoli  is  at  first  entirely  of  the  foetal-cell  type,  the  large 
flat  respiratory  plates  appearing  only  late  in  foetal  life.     Just  how  and  when 


_  IiG.  213.— Scheme  of  Development  of  Lung  (Right),  h,  b,  b,  thethree primary  bron- 
chial buds;  b',  b',  b',  collateral  branches  and  secondary  buds,  terminating  in  vpp,  the 
primary  vesicles;  vpd,  pulmonary  vesicles  proper  or  alveoli;  ca,  alveolar  canals.     The 

broken  line limits  the  stage  of  the  three  primary  lung  buds;  between  this  line 

and  the  Hne only  the  three  primary  buds,  their  collaterals  and  secondary  buds; 

between  the  hne and  hne  ,  the  stage  of  dichotomous  division  and  of 

termination  in  primary  vesicles.  Up  to  this  point  the  development  is  that  of  a  com- 
pound alveolar  gland.  From  this  hne  to  the  surface  represents  the  final  period  of 
development,  which  is  peculiar  to  the  lung  and  results  in  the  formation  of  the  pulmonary 
alveoli.     (Prenant.j 

the  flattening  of  the  epithelial  cells  takes  place  is  not  definitely  known.  The 
accepted  theory  has  been  that  the  cells  become  flattened  rather  suddenly  at  birth 
as  a  result  of  the  first  inspiration.  Some  authors  describe  a  gradual  thinning  of 
the  ceUs  from  the  sixth  foetal  month  on.  Bikfalir  describes  a  gradual  thinning 
which  is  completed  rather  rapidly  on  inspiration.  The  foetal  and  respiratory 
cells  of  the  adult  lung  have  the  same  embryonic  origin.  During  the  early  stages 
of  lung  development  the  mesodermic  tissue  predominates,  but  with  the  rapid 
growth  of  the  tubules  the  proportion  of  the  two  changes  until  in  the  adult 
lung  the  mesodermic  tissue  becomes  restricted  to  the  inconspicuous  pulmonary 
framework  and  the  blood-vessels. 


THE  RESPIRATORY  SYSTEM  317 

TECHNIC 

(i)  The  technic  for  the  largest  bronchi  is  the  same  as  for  the  trachea  (technic 
3,  p.  304).  The  medium  size  and  small  bronchi  are  studied  in  sections  of  the 
lung. 

(2)  Lung  and  Bronchi. — Carefully  remove  the  lungs  and  trachea  (human, 
dog,  or  cat)  and  tie  into  the  trachea  a  cannula  to  which  a  funnel  is  attached. 
Distend  the  lungs  moderately  (pressure  of  two  to  four  inches)  by  pouring  in 
formalin-Miiller's  fluid  (technic  5,  p.  7),  and  then  immerse  the  whole  in  the  same 
fixative  for  twenty-four  hours.  Cut  into  small  blocks,  using  a  very  sharp  razor 
so  as  not  to  squeeze  the  tissue,  harden  in  alcohol,  stain  thin  sections  with  haema- 
toxylin-eosin  (technic  i,  p.  20),  and  mount  in  balsam  or  in  eosin-glycerin.  The 
larger  bronchi  are  found  in  sections  near  the  root  of  the  lung.  The  arrangement 
of  the  pulmonary  lobules  is  best  seen  in  sections  near  and  horizontal  to  the  sur- 
face. Sections  perpendicular  to  and  including  the  surface  show  the  pulmonary 
pleura. 

(3)  Respiratory  Epithelium  (technic  i,  p.  78). 

(4)  Elastic  Tissue  of  the  Lung  (technic  3,  p.  28). 

(5)  Blood-vessels. — For  the  study  of  the  blood-vessels,  especially  of  the  cap- 
illary networks  of  the  alveoli,  sections  of  injected  lung  should  be  made.  A  fresh 
lung  is  injected  (page  25)  with  blue  gelatin,  through  the  pulmonary  artery. 
It  is  then  hardened  in  alcohol,  embedded  in  celloidin,  and  thick  sections  are 
stained  with  eosin  and  mounted  in  balsam. 

General  References  for  Further  Study 

Miller,  W.  S.:  Das  Lungenlappchen,  seine  Blut-  und  Lymphgefasse. 
Councilman:  The  Lobule  of  the  Lung  and  its  Relations  to  the  Lymphatics. 
Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 


CHAPTER  VIII 
THE  URINARY  SYSTEM 

The  Kidney 

The  kidney  is  a  compound  tubular  gland.  It  is  enclosed  by  a 
firm  connective-tissue  capsule,  the  inner  layer  of  which  contains 
smooth  muscle  cells.     In  many  of  the  lower  animals  and  in  the  human 

foetus  septa  extend  from  the  cap- 
sule into  the  gland,  dividing  it 
into  a  number  of  lobes  or  renculi. 
In  some  animals,  e.g.,  the  guinea- 
pig  and  rabbit,  the  entire  kidney 
consists  of  a  single  lohe  (Fig.  214). 
In  the  adult  human  kidney  the 
division  into  lobes  is  not  complete, 
the  peripheral  parts  of  the  differ- 
ent lobes  blending.  Rarely  the 
foetal  division  into  lobes  persists 
«  ,     ,,  ^.32^.,™^^         in  adult  life,  such  a  kidney  being 

V^i  '        ?3.        known  as  a  "lobulated  kidney." 

On  the  mesially  directed  side  of 
the  kidney  is  a  depression  known 
as  the  hilum  (Fig.  214).  This 
serves  as  the  point  of  entrance  of 
the  renal  artery  and  of  exit  for  the 
renal  vein  and  ureter. 

On  section,  a  division  of  the 
organ  into  two  zones  is  apparent 
to  the  naked  eye  (Figs.  214  and 
215).  The  outer  zone  or  cortex 
has  a  granular  appearance,  while 
the  inner  zone  or  medulla  shows  radial  striations.  This  difference 
in  appearance  between  cortex  and  medulla  is  mainly  due,  as  will  be 
seen  subsequently,  to  the  fact  that  in  the  cortex  the  kidney  tubules 
are  convoluted,  while  in  the  medulla  they  run  in  parallel  radial  hues 

318 


Fig.  214. — Longitudinal  Section 
Through  Kidney  of  Guinea-pig,  includ- 
ing hilum  and  beginning  of  ureter.  XS- 
(Technic  i,  p.  331.)  a,  Pelvis;  h,  papilla; 
c,  wall  of  pelvis;  d,  ureter;  e,  ducts  of 
Bellini;  /,  cortical  pyramids;  g,  medullary 
rays;  h,  cortex;  i,  medulla;  j,  renal  cor- 
puscles. 


THE  URINARY  SYSTEM 


319 


alternating  with  straight  blood-vessels.  The  medullary  portion  of 
the  kidney  projects  into  the  pelvis,  or  upper  expanded  beginning  of 
the  ureter  (Figs.  214  and  215)  in  the  form  of  papillcB.     The  number 


Fig.  215. 


Fig.  216. 


Fig.  215. — Longiludinal  Section  of  Kidney  Through  Hilum.  a,  Cortical  pyramid; 
b,  medullary  ray;  c,  medulla;  d,  cortex;  e,  renal  calyx;/,  hilum;  g,  ureter;  //,  renal  artery; 
i,  obliquely  cut  tubules  of  medulla;  j  and  k,  renal  arches;  I,  column  of  Bertini;  m, 
connective  tissue  and  fat  surrounding  renal  vessels;  71,  medulla  cut  obliquely;  0,  papilla; 
p,  medullary  pyramid.     CMerkel-Henle.) 

Fig.  216. — Scheme  of  Uriniferous  Tubule  and  of  the  Blood-vessels  of  the  Kidney 
showing  their  relation  to  each  other  and  to  the  different  parts  of  the  kidney.  G,  Glomer- 
ulus; he,  Bowman's  capsule;  N,  neck;  I'C,  proximal  convoluted  tubule;  S,  spiral 
tubule;  D,  descending  arm  of  Henle's  loop;  L,  Henle's  loop;  A,  ascending  arm  of  Hcnle's 
loop;  I ,DC,  distal  convoluted  tubule;  AC,  arched  tubule;  SC,  straight  collecting  tubule; 
ED,  duct  of  BeUini;  A,  arcuate  artery,  and  V ,  arcuate  vein,  giving  off  interlobular  vessels 
to  cortex  and  vasa  recta  to  medulla;  a,  afferent  vessel  of  glomerulus;  e,  elTercnt  vessel  of 
glomerulus;  c,  capillary  network  in  cortical  labyrinth;  .v,  stellate  veins;  vr,  vasa  recta  and 
caijillary  network  of  medulla.     fPearsol.) 

of  j)apilla;  varies  from  ten  to  fifteen,  corresponding  to  the  number 
of  lobes  in  the  fcxtal  kidney.  The  pyramidal  segment  of  medulla, 
the  apex   of   which   is  a  papilla — in  other   words,   the   medullary 


320  THE  ORGANS 

portion  of  a  foetal  lobe — is  known  as  a  medullary  or  Malpighian 
pyramid.  The  extensions  downward  of  cortical  substance  between 
the  Malpighian  pyramids  constitute  the  columns  of  Bertini  or  septa 
renis.  Radiating  lines — medullary  rays  or  pyramids  of  Ferrein — - 
extend  outward  from  the  base  of  each  Malpighian  pyramid  into  the 
cortex  (Fig.  215).  As  the  rays  extend  outward  in  groups  they 
outline  pyramidal  cortical  areas.  These  are  known  as  the  cortical 
pyramids  or  cortical  labyrinths. 

The  secreting  portion  of  the  kidney  is  composed  of  a  large  number 
of  long  tortuous  tubules,  the  uriniferous  tubules. 

Each  URINIFEROUS  TUBULE  begins  in  an  expansion  known  as 
Bowman's  capsule  (Figs.  216,  BC,  and  217,  3,  4,  5).     This  encloses  a 


f 

Fig.  217. — Diagrams  Illustrating  Successive  Stages  in  Development  of  the  Renal 
Corpuscle,  i  and  2,  Approach  of  blood-vessel  and  blind  end  of  tubule;  3,  invagination  of 
tubule  by  blood-vessels;  4  and  5,  later  stages,  showing  development  of  glomerulus  and  of 
the  two-layered  capsule  of  the  renal  corpuscle,  the  outer  layer  being  the  capsule  of 
Bowman  continuous  with  the  epithelium  of  the  first  convoluted  tubule. 

tuft  of  blood  capillaries,  the  glomerulus.  Bowman's  capsule  and  the 
glomerulus  together  constitute  the  Malpighian  body  or  renal  corpuscle 
(Fig.  218).  As  it  leaves  the  Malpighian  body  the  uriniferous  tubule 
becomes  constricted  to  form  the  neck  (Figs.  216,  N,  217,  and  218,  b). 
It  next  broadens  out  into  a  greatly  convoluted  portion,  the  first  con- 
voluted tubule  (Fig.  216,  PC,  and  Fig.  219).  The  Malpighian  body, 
the  neck,  and  the  first  convoluted  tubule  are  situated  in  the  cortical 
pyramid  (Fig.  216).  The  tubule  next  takes  a  quite  straight  course 
downward  into  the  medulla — descending  arm  of  Henle's  loop  (Fig.  216, 
D) — turns  sharply  upon  itself — Henle's  loop  (Fig.  216,  L) — and  passes 
again  toward  the  surface — ascending  arm  of  Henle's  loop  (Fig.  216, 
A ) — through  the  medulla  and  medullary  ray.  Leaving  the  medullary 
ray,  it  enters  the  same  cortical  pyramid  from  which  it  took  origin  to 
become  the  second  convoluted  tubule  (Fig.  216,  DC).     This  tubule  is  in 


THE  URINARY  SYSTEM  321 

close  proximity  to  the  Malpighian  body  from  which  it  started,  lying, 
however,  on  the  side  of  the  afferent  and  efferent  blood-vessels,  i.e.,  on 
the  side  opposite  its  point  of  origin.  The  second  convoluted  tubule 
passes  into  the  arched  tubule  (AC)  which  enters  a  medullary  ray  and 
continues  straight  down  through  the  medullary  ray  and  medulla  as 
the  straight  or  collecting  tubule  (SC).  During  its  course  the  col- 
lecting tubule  receives  other  arched  tubules.  As  it  descends  it  be- 
comes broader,  enters  the  papilla,  where  it  is  known  as  the  duct  of 
Bellini  (ED),  and  opens  on  the  surface  of  the  papilla  into  the  kid- 
ney pelvis.  About  twenty  ducts  of  Bellini  open  upon  the  surface  of 
each  papilla,  their  openings  being  known  as  the  foramina  papillaria. 


/ 


Fig.  2i8. — Malpighian  Body  from  Human  Kidney.     X280.     (Technic  2,  p.  331.)     a, 
Bowman's  capsvde;  i,  neck;  c,  first  convoluted  tubule;  d,  afferent  and  efferent  vessels. 

Each  tubule  consists  of  a  delicate  homogeneous  membrana  propria 
upon  which  rests  a  single  layer  of  epithelial  cells.  The  shape  and 
structure  of  the  epithelium  differ  in  different  portions  of  the  tubule. 

I.  The  Malpighian  body  is  spheroidal,  and  has  a  diameter  of  from 
120  to  200//.  The  structure  of  the  Malpighian  body  can  be  best 
understood  by  reference  to  its  development  (Fig.  217).  During  the 
development  of  the  uriniferous  tubules  and  of  the  blood-vessels  of  the 
kidney,  the  growing  end  of  a  vessel  meets  the  growing  end  of  a  tubule 
in  such  a  way  that  there  is  an  invagination  of  the  tubule  by  the  blood- 
vessel (see  Fig.  217).  The  result  is  that  the  end  of  the  vessel  which 
develops  a  tuft-like  network  of  capillaries — the  glomerulus — comes  to 
lie  within  the  expanded  end  of  the  tubule,  which  thus  forms  a  two- 
layered  capsule  for  the  glomerulus.  One  layer  of  the  capsule  closely 
invests  the  tuft  of  capillaries,  dipping  down  into  it  and  separating  the 
21 


322  THE  ORGANS 

groups  of  capillaries  (see  p.  326).  This  layer  by  modification  of  the 
original  epithelium  of  the  tubule  is  finally  composed  of  a  single  layer 
of  flat  epithelial  cells  with  projecting  nuclei.  The  outer  layer  of  the 
capsule  lies  against  the  delicate  connective  tissue  which  surrounds 
the  Malpighian  body.  This  layer  consists  of  a  similar  though  slightly 
higher  epithelium  and  is  known  as  Bowman's  capsule.  Between  the 
glomerular  layer  of  the  capsule  and  Bowman's  capsule  proper  is  a 
space  which  represents  the  beginning  of  the  lumen  of  the  uriniferous 
tubule  (Fig.  218),  the  epithelium  of  Bowman's  capsule  being  directly 
continuous  with  that  of  the  neck  of  the  tubule. 

B 


A 

Fig.  219. — Proximal  Convoluted  Tubules  of  Human  Kidney.     X350.     (Technic  2, 

P-  33I-)     ^,  Cross-section;  B,  oblique  section. 

• 

2.  The  Neck. — This  is  short  and  narrow,  and  is  lined  by  a  few 
cuboidal  epithelial  cells.  Toward  its  glomerular  end  the  epithelium 
is  transitional  between  the  fiat  epithelium  of  Bowman's  capsule  and 
the  cuboidal  epithelium  of  the  neck  proper.  At  its  other  end  the 
epithelium  of  the  neck  becomes  larger  and  more  irregular  as  it  passes 
over  into  that  lining  the  next  division  of  the  tubule  (Fig.  218). 

3.  The  first  convoluted  tubule  (Fig.  219)  measures  from  40  to  70/* 
in  diameter.  It  is  lined  by  irregularly  cuboidal  or  pyramidal  epithe- 
lium, with  very  indistinct  demarcation  between  the  cells.  The  cyto- 
plasm is  granular,  and  the  granules  are  arranged  in  rows,  giving  the 
cell  a  striated  appearance.  This  is  especially  marked  at  the  basal 
end  of  the  cell  where  the  nucleus  is  situated.  A  zone  of  fine  striations 
along  the  free  surface  frequently  presents  somewhat  the  appearance 
of  cilia. 

4.  The  descending  arm  of  Henle's  loop  is  narrow  (Fig.  220,  i), 
10  to  15/^  in  diameter.     It  is  lined  by  a  simple  fiat  epithelium.     The 


THE  URINARY  SYSTEM 


323 


part  of  the  cell  which  contains  the  nucleus  bulges  into  the  lumen,  and 
as  the  nuclei  of  opposite  sides  of  the  tubule  usually  alternate,  the 
lumen  is  apt  to  present  a  wavy  appearance  in  longitudinal  sections. 
5.  Henle's  Loop. — The  epithelium  here  changes  from  the  flat  of 
the  descending  arm  to  the  cuboidal  of  the  ascending  arm.  The  exact 
point  w^here  the  transition  occurs  varies.  It  may  take  place  during 
the  turn  of  the  loop,  or  in  either  the  ascending  or  descending  arm. 


M 


#i 


M. 


s^ 


Fig.  220. — Tubules  of  Human  Kidney.  Xs6o.  From  longitudinal  section. 
(Technic  2,  p.  331.)  i,  Descending  arm  of  Henle's  loop;  2,  ascending  arm  of  Henle's 
loop;  3,  collecting  tubule;  4,  duct  of  Bellini.  Beneath  the  longitudinal  sections  are  seen 
cross  sections  of  the  same  tubules. 

6.  The  ascending  arm  of  Henle's  loop  (Fig.  220,  2)  is  broader 
than  the  descending,  measuring  from  20  to  30/(  in  diameter.  Its 
epithelium  is  cuboidal  with  granular  striated  protoplasm.  The  cells 
thus  resemble  those  of  the  convoluted  tubule,  but  are  smaller,  more 
regular,  and  less  granular. 

7.  The  second  convoluted  tubule  has  a  diameter  of  40  to  50/^.  It  is 
much  less  tortuous  than  the  first  convoluted  tubule.  Its  epithelium 
is  similar  to  that  lining  the  first  convoluted  tubule  except  that  it  is 
slightly  lower  and  less  distinctly  striated. 

8.  The  arched  tubule  has  a  somewhat  narrower  lumen  (about  25/O 
than  the  seccmd  convoluted.  It  is  lined  with  a  low  cuboidal  epithe- 
lium with  only  slightly  granular  cytoplasm. 


324 


THE  ORGANS 


9.  The  straight  or  collecting  tubule  (Fig.  2  20, 3)  has  at  its  commence- 
ment at  the  apex  of  a  medullary  ray  a  diameter  of  from  40  to  50/t. 
As  it  descends  it  receives  other  arched  tubules,  and  increases  in 
diameter  until  in  the  ducts  of  Bellini  (Fig.  220,  4)  of  the  papilla  it  has 
a  diameter  of  from  200  to  300/^  and  a  widely  open  lumen.  The 
epithelium  is  at  first  low  and  gradually  increases  in  height.     In  the 


X 


■■:^ 


Fig.  2  2i.^Cross  Section  Through  Cortex  of  Human  Kidney.  X60.  (Technic  2, 
P-  33I-)  o>  Convoluted  tubules  of  cortical  pyramid;  b,  interlobular  artery;  c,  medullary 
rays;  d,  Malpighian  bodies. 

ducts  of  Bellini  it  is  of  the  high  columnar  type.  The  cytoplasm  of 
these  cells  contains  comparatively  few  granules,  thus  appearing 
transparent  in  contrast  with  the  granular  cytoplasm  of  the  ascending 
arms  of  Henle's  loops  and  of  the  convoluted  tubules. 


Location  in  kidney 


Cortical  labyrinth  .  . . .   < 


Portion  of  tubule  Epithelium 

Bowman's  capsule. .   Flat  with  bulging  nuclei. 

Neck Cuboidal,  granular. 

First  convoluted Pyramidal,  granular;  large  cells 

with  granules  in  rows, 
giving  striated  appearance; 
striated  free  border;  indis- 
tinct cell  outline. 

Second  convoluted. .  Similar  to  preceding,  but  cells 
not  so  distinctly  striated  and 
more  regular  in  shape. 


THE  URINARY  SYSTEM 


325 


Location  in  kidnev 


Medullary  ray  in  cor- 
tex 


Portion  of  tubule  Epithelium 

Arched  (passing  from  Rather  clear  cuboidal  cells, 
labyrinth  to  ray) 
Part    of    ascending     Cuboidal,  granular,  regular, 
arm     of     Henle's 
loop 
Collecting  tubule. .  .    Cuboidal    or    columnar,    clear; 
varying  in  height  with  diameter 
of  tubule. 


Descending       arm,  Clear    flat    cells    with    bulging 
Henle's  loop  nuclei. 

Henle's  loop Usually  like  descending,  rarely 

like  ascending  arm. 
*!   Part     of     ascending  Cuboidal,  granular. 
I     arm  Henle's  loop 

Collecting  tubule.  .  .    Cuboidal    or    columnar,    clear; 
I  varying    in    height    with   di- 

[  ameter  of  tubule. 

Papilla Ducts  of  Bellini Clear,     cuboidal     or    columnar 

cells  according  to  diameter  of 
tubule. 


Medulla. 


The  epithelium  of  the  uriniferous  tubule  rests  upon  an  apparently 
structureless  basement  membrane.  Rlihle  describes  the  basement 
membrane  as  consisting  of  delicate  longitudinal  and  circular  connec- 
tive-tissue fibrils.  He  regards  the  fibrils  as  merely  a  more  regular 
arrangement  of  the  interstitial  connective  tissue.  According  to 
Riihle  the  epithelium  simply  rests  upon  the  basement  membrane, 
being  in  no  way  connected  with  it.  In  the  cortex  the  tubules  are 
closely  packed  and  the  amount  of  interstitial  connective  tissue  is 
extremely  small.  In  the  medulla  the  connective  tissue  is  more 
abundant. 

(Jf  the  function  of  the  different  parts  of  the  uriniferous  tubule  our 
knowledge  is  extremely  limited.  The  water  of  the  urine  is  secreted 
in  the  Malpighian  body,  some  specific  action  of  the  cells  covering  the 
glomerulus,  allowing  the  water,  normally  free  from  albumen,  to  pass 
from  the  capillaries  into  the  lumen  of  the  tubule.  The  urinary  solids 
are  secreted  mainly  or  wholly  by  the  cells  of  the  convoluted  tubule 
and  of  the  ascending  arm  of  Henle's  loop. 

Blood-vessels  (diagram,  Fig.  223).— The  blood  supply  to  the 
kidney  is  rich  and  the  blood-vessels  come  into  intimate  relations  with 
the  tubules.     The  renal  artery  enters  the  kidney  at  the  hilum,  and 


326  THE  ORGANS 

immediately  splits  up  into  a  number  of  branches — the  interlobar 
arteries  (Fig.  223,  g).  These  give  off  twigs  to  the  calyces  and  to  the 
capsule,  then  without  further  branching  pass  between  the  papillae 
through  the  medulla  to  the  junction  of  medulla  and  cortex.  Here 
they  bend  sharply  at  right  angles  and  following  the  boundary  line 
between  cortex  and  medulla,  form  a  series  of  arches,  the  arteries 
arciformes  or  arcuate  arteries  (Fig.  223,  d).  From  the  arcuate  arteries 
two  sets  of  vessels  arise,  one  supplying  the  cortex,  the  other  the  me- 
dulla (Figs.  216  and  223). 


d  < 


b  c 

Fig.  222 — Cross  Section  through  Medulla  of  Human  Kidney.  X465.  (Technic  2, 
p.  331.)  a,  Capillaries;  b,  collecting  tubule;  c,  ascending  arms  of  Henle's  loops;  d,  de- 
scending arms  of  Henle's  loops. 

The  arteries  to  the  cortex  spring  from  the  outer  (Fig.  223,  h)  sides  of 
the  arterial  arches,  and  as  interlobular  arteries  pursue  a  quite  straight 
course  through  the  cortical  pyramids  toward  the  surface,  about  mid- 
way between  adjacent  medullary  rays.  From  each  interlobular  artery 
are  given  off  numerous  short  lateral  branches,  each  one  of  which 
passes  to  a  Malpighian  body.  Entering  a  Malpighian  body  as  its 
afferent  vessel,  the  artery  breaks  up  into  a  number  of  small  arterioles, 
which  in  turn  give  rise  to  the  groups  of  capillaries  which  form  the 


THE  URINARY  SYSTEM 


327 


glomerulus.  Each  group  of  glomerular  capillaries  arising  from  a 
single  arteriole  is  separated  from  its  neighbors  by  a  rather  larger 
amount  of  connective  tissue  than  that  which  separates  the  individual 
capillaries.  This  gives  to  the  glomerulus  its  lobular  appearance. 
From  the  smaller  glomerular  capillaries  the  blood  passes  into  some- 


Fir    22^  — Diacram  to  IllusLralc  (left)  the  Course  of  the  Uriniferous  Tubule;  (right) 
g,  interlobar  artery;  h,  medulla;  /,  medullary  ray;;,  cortex. 

what  larger  capillaries,  which  unite  to  form  the  efferent  vessel  of  the 
gh)merulus.  As  afferent  and  efferent  vessels  He  side  by  side,  the 
glomerulus  has  the  appearance  of  being  suspended  from  this  pomt 
(Figs  2 1 6  2 1 8) .    rite  entire  vascular  system  of  the  glomerulus  is  arterial. 


328  THE  ORGANS 

After  leaving  the  glomerulus,  the  efferent  vessel  breaks  up  into  a 
second  system  of  capillaries,  which  form  a  dense  network  among  the 
tubules  of  the  cortical  pyramids  and  of  the  medullary  rays.  The 
mesh  corresponds  to  the  shape  of  the  tubules,  being  irregular  in  the 
pyramids,  long  and  narrow  in  the  rays.  In  these  capillaries  the  blood 
gradually  becomes  venous  and  passes  into  the  interlobular  veins  (Fig. 
223,  c).  These  accompany  the  interlobular  arteries  to  the  boundary 
between  cortex  and  medulla,  where  they  enter  the  arcuate  veins,  which 
accompany  the  arcuate  arteries  (Fig.  223,  d). 

The  main  arteries  to  the  medulla  arise  from  the  inner  concave  sides 
of  the  arterial  arches.  They  pass  straight  down  among  the  tubules 
of  the  medulla  and  are  known  as  arterice  rectce.  Branching,  they  give 
rise  to  a  long-meshed  capillary  network  which  surrounds  the  tubules. 
This  capillary  network  is  also  supplied  by  (i)  efferent  vessels  from 
the  more  deeply  situated  glomeruli  (false  arteriae  rectae)  and  (2)  by 
medullary  branches  from  the  interlobular  arteries.  The  veins  of  the 
medulla  arise  from  the  capillary  network  and  follow  the  arteries 
back  to  the  junction  of  medulla  and  cortex,  where  they  empty  into 
the  arcuate  veins  (Fig.  223,  d). 

In  addition  to  the  distribution  just  described,  some  of  the  inter- 
lobular arteries  extend  to  the  surface  of  the  kidney,  where  they  enter 
the  capsule  and  form  a  network  of  capillaries  which  anastomose  with 
capillaries  of  the  suprarenal,  recurrent,  and  phrenic  arteries.  A 
further  collateral  circulation  is  established  by  branches  of  the  above- 
named  arteries  penetrating  the  kidney  and  forming  capillary  networks 
within  the  cortex,  even  supplying  some  of  the  more  superficial 
glomeruli.  The  most  superficial  of  the  small  veins  which  enter  the 
interlobular  are  arranged  in  radial  groups,  having  the  interlobular 
veins  as  their  centres.  These  lie  just  beneath  the  capsule,  and  are 
known  as  the  stellate  veins  of  Verheyn.  In  addition  to  capillary 
anastomoses,  direct  communication  between  arteries  and  veins  of 
both  cortex  and  medulla,  by  means  of  trunks  of  considerable  size, 
has  been  described. 

The  lymph  vessels  of  the  kidney  are  arranged  in  two  systems,  a 
superficial  system  which  ramifies  in  the  capsule,  and  a  deep  system 
w^hich  accompanies  the  arteries  to  the  parenchyma  of  the  organ. 
Little  is  known  of  the  relation  of  the  lymphatics  to  the  kidney  tubules. 

Nerves. — These  are  derived  from  both  cerebro- spinal  and  sym- 
pathetic systems.  The  medullated  fibres  appear  to  pass  mainly  to 
the  walls  of  the  blood-vessels  which  supply   the  kidney   capsule. 


THE  URIXARY  SYSTEM  329 

Plexuses  of  fine  non-medulla  ted  fibres  (sympathetic)  accompany  the 
arteries  to  the  glomeruli.  Delicate  terminals  have  been  described  as 
passing  from  these  plexuses,  piercing  the  basement  membrane  and 
ending  freely  between  the  epithelial  cells  of  the  tubules. 

The  Kidney-Pelvis  and  Ureter 

The  kidney-pelvis,  with  its  subdivisions  the  calyces,  and  the  ureter 
constitute  the  main  oxcretory  duct  of  the  kidney.  Their  walls  consist 
of  three  coats:  an  inner  mucous,  a  middle  muscular,  and  an  outer 
fibrous. 

The  mucosa  is  lined  by  epithelium  of  the  transitional  type. 
There  are  from  four  to  eight  layers  of  cells,  the  cell  outlines  are  usually 
well  defined,  and  the  surface  cells  instead  of  being  distinctly  squamous 
are  only  slightly  flattened.  Less  commonly  large  flat  plate-like 
cells,  each  containing  several  nuclei,  are  present.  The  cells  rest  upon 
a  basement  membrane,  beneath  which  is  a  stroma  of  delicate  fibro- 
elastic  tissue  rich  in  cells.  Diffuse  lymphatic  tissue  frequently 
occurs  in  the  stroma,  especially  of  the  pelvis.  Occasionally  the 
lymphatic  tissue  takes  the  form  of  small  nodules.  Mucous  glands 
in  small  numbers  are  found  in  the  stroma  of  the  pelvis  and  upper 
part  of  the  ureter.  There  is  no  distinct  submucosa,  although  the 
outer  part  of  the  stroma  is  sometimes  referred  to  as  such. 

The  muscularis  consists  of  an  inner  longitudinal  and  an  outer 
circular  layer.  In  the  lower  part  of  the  ureter  a  discontinuous  outer 
longitudinal  layer  is  added. 

The  fibrosa  consists  of  loosely  arranged  connective  tissue  and 
contains  many  large  blood-vessels.  It  is  not  sharply  limited  exter- 
nally, but  blends  with  the  connective  tissue  of  surrounding  structures, 
and  serves  to  attach  the  ureter  to  the  latter. 

The  larger  blood-vessels  run  in  the  fibrous  coat.  From  these, 
branches  pierce  the  muscular  layer,  give  rise  to  a  capillary  network 
among  the  muscle  cells,  and  then  pass  to  the  mucosa,  in  the  stroma 
of  which  they  break  up  into  a  rich  network  of  capillaries.  The  veins 
follow  the  arteries. 

The  lymphatics  follow  the  blood-vessels,  being  especially  numer- 
ous in  the  stroma  of  the  mucosa. 

Nerves. — Plexuses  of  both  medullated  and  non-medullated  fibres 
occur  in  the  walls  of  the  ureter  and  pelvis.  The  non-medullated 
fibres  pass  mainly  to  the  cells  of  the  muscularis.     Medullated  fibres 


330  THE  ORGANS 

enter  the  mucosa  where  they  lose  their  medullary  sheaths.     Terminals 
of  these  fibres  have  been  traced  to  the  lining  epithelium. 

The  Urinary  Bladder 

The  walls  of  the  bladder  are  similar  in  structure  to  those  of  the 
ureter. 

The  mucous  membrane  is  thrown  up  into  folds  or  is  compara- 
tively smooth,  according  to  the  degree  of  distention  of  the  organ. 
The  epithelium  is  of  the  same  general  type — transitional  epithelium 


Fig.  224. — Vertical  Section  through  Wall  of  moderately  distended  Human  Bladder. 
X60.  (Technic  5,  p.  331.)  a,  Epithelium,  b,  stroma,  of  mucous  membrane;  c,  sub- 
mucosa;  d,  inner  muscle  layer;  e,  middle  muscle  layer;/,  outer  muscle  layer. 

(see  page  74) — as  that  of  the  ureter.  The  number  of  layers  of  cells 
and  the  shapes  of  the  cells  depend  largely  upon  whether  the  bladder 
is  full  or  empty.  In  the  collapsed  organ  the  superficial  cells  are 
cuboidal  or  even  columnar,  their  under  surfaces  being  marked  by 
pit-like  depressions  caused  by  pressure  of  underlying  cells.  Beneath 
the  superficial  cells  are  several  layers  of  polygonal  cells,  while  upon 
the  basement  membrane  is  the  usual  single  layer  of  small  cuboidal 
cells.     In   the  moderately  distended  bladder   the  superficial  cells 


THE  URIXARY  SYSTEM  331 

become  flatter  and  the  entire  epithelium  thinner  (Fig.  224).  In  the 
distended  organ  there  is  still  further  flattening  of  the  superficial  cells 
and  thinning  of  the  entire  epithelium.  The  stroma  consists  of  line 
loosely  arranged  connective  tissue  containing  many  lymphoid  cells 
and  sometimes  small  lymph  nodules.  It  merges  without  distinct 
demarcation  into  the  less  cellular  siihmucosa  (Fig.  224,  c). 

The  three  muscular  layers  of  the  lower  part  of  the  ureter  are  con- 
tinued on  to  the  bladder,  where  the  muscle  bundles  of  the  different 
layers  interlace  and  anastomose,  but  can  be  still  indistinctly  differ- 
entiated into  an  inner  longitudinal,  a  middle  circular,  and  an  outer 
longitudinal  layer  (Fig.  224,  d,  e,f). 

The  fibrous  layer  is  similar  to  that  of  the  ureter,  and  attaches  the 
organ  to  the  surrounding  structures. 

The  blood-  and  l5rmph -vessels  have  a  distribution  similar  to  those 
of  the  ureter. 

Nerves. — Sensory  medullated  fibres  pierce  the  muscularis,  branch 
repeatedly  in  the  stroma,  lose  their  medullary  sheaths,  and  terminate 
among  the  cells  of  the  lining  epithelium.  Sympathetic  fibres  form 
plexuses  in  the  fibrous  coat,  where  they  are  interspersed  with  numerous 
small  groups  of  ganglion  cells.  Axones  of  these  sympathetic  neurones 
penetrate  the  muscularis.  Here  they  form  plexuses,  from  which  are 
given  off  terminals  to  the  individual  muscle  cells. 

For  development  of  urinary  system  see  page  376. 


TECHNIC 

(i)  Fix  the  simple  kidney  of  a  rabbit  or  guinea-pig  in  formalin- Aliiller's  fluid 
(technic  5,  p.  7).  Make  sections  through  the  entire  organ  including  the  papilla 
and  pelvis,  stain  with  haematoxylin-eosin  (technic  i,  p.  20),  and  mount  in  balsam. 
This  section  is  for  the  study  of  the  general  topography  of  the  kidney. 

(2)  Fix  small  pieces  from  the  different  parts  of  a  human  kidney  in  formalin- 
Mullcr's  fluid  or  in  Zenker's  fluid.  Thin  sections  should  be  made,  some  cutting 
the  tubules  longitudinally,  others  transversely,  stained  with  ha;matoxylin-eosin 
and  mounted  in  balsam. 

(3)  Blood-vessels. — For  the  purpose  of  demonstrating  blood-vessels  of  the 
kidney  the  method  of  double  injection  is  useful  (page  26). 

(4)  Ureter. — Cut  transversely  into  short  segments,  fix  in  formalin-Muller's 
fluid  (technic  5,  p.  7),  and  stain  transverse  sections  with  ha;matoxylin-cosin 
(technic  i,  p.  20),  or  with  hacmatoxylin-picro-acid-fuchsin  (technic  .3,  p.  21). 
Mount  in  balsam. 

(5)  Bladder  (technic  i,  p.  254,  or  technic  2,  [>.  254).  By  the  latter  method 
any  desired  degree  of  distention  may  Ijc  obtained. 


332  THE  ORGANS 

General  References  for  Further  Study 

Kolliker:  Handbuch  der  Gewebelehre,  vol.  iii. 

Gegenbauer:  Lehrbuch  der  Anatomic  des  Menschen,  vol.  ii. 

Henle:  Handbuch  der  Anatomic  dcs  Menschen,  vol.  ii. 

Johnston:  A  Reconstruction  of  a  Glomerulus  of  the  Human  Kidney.     Johns 
Hopkins  Hosp.  Bui.,  vol.  xi.,  1900. 

Miiller:  Ueber    die    Ausscheidung    des    Methylenblau    durch    die    Nieren. 
Deutsches  Archiv  f.  klin.  Med.,  Bd.  63,  1899. 


CHAPTER  IX 

THE  REPRODUCTIVE  SYSTEM 

I.  MALE  ORGANS 

The  Testis 

The  testes  are  compound  tubular  glands.  Each  testis  is  enclosed 
in  a  dense  connective- tissue  capsule,  the  tunica  alhuginea  (Fig.  225,  a). 
Outside  the  latter  is  a  closed  serous  sac,  the  tunica  vaginalis,  the 
visceral  layer  of  which  is  attached  to 
the  tunica  albuginea,  while  the  parietal 
layer  lines  the  inner  surface  of  the 
scrotum.  Posteriorly  the  serous  sac 
is  wanting,  the  testis  lying  behind  and 
outside  of  the  tunica  vaginalis.  As  the 
latter  is  derived  from  the  peritoneum, 
being  brought  down  with  and  invagi- 
nated  by  the  testes  in  their  descent  to 
the  scrotum,  it  is  lined  by  mesothelial 
cells.  To  the  inner  side  of  the  tunica 
albuginea  is  a  layer  of  loose  connective 
tissue  rich  in  blood-vessels,  the  tunica 
vasculosa.  Posteriorly  the  tunica  albu- 
ginea is  greatly  thickened  to  form  the 
corpus  Highmori,  or  mediastinum  testis, 
from  which  strong  connective-tissue 


septa  radiate  (Figs.  225,  m  and  226,  b). 


Fig.  225. — Diagram  illustrating 
the  Course  and  Relations  of  the  Semi- 
niferous Tubules  and  their  Excretory 
Ducts.  (Piersol.)  a,  Tunica  albu- 
ginea; b,  connective-tissue  septum 
between  lobules;  w,  mediastinum;  t, 
convoluted  portion  of  seminiferous 
These  septa  pass  completely  through  tubule;  s,  straight  tulmlc;  r,  rate 
fViA  nr<Tc»n   anri    hlonrl    witVi  fhf^  tnmVp     testis;  e,  vasa  elTerentia;  c,  tubules 

tne  organ  and  blena  witn  tne  tunica   ^^f  j^^^^  ^^  epididymis;  ic,  vas  epi- 

albuginca    at  various  points.      In  this    didymis;   vd,   vas   deferens;   va,   vas 
.       .    ^      .  ,  ,,       _        .    .         ,    T      aberrans; />,  paradidymis. 

way  the  mterior  of  the  testis  is  subdi- 
vided into  a  number  of  pyramidal  chambers  or  lobules,  with  bases 
directed  toward  the  periphery  and  apices  at  the  mediastinum  (Figs. 
225  and  226). 

Behind  the  testis  and  outside  of  its  tunica  albuginea  is  an  elongated 
body — the  epididymis  (Figs.  225,  c  and  226,  c),  consisting  of  convoluted 

333 


334 


THE  ORGANS 


>. 


■'■I^^i^^*^ 


tubules  continuous  with  those  of  the  mediastinum.  The  epididymis  is 
divided  into  three  parts:  an  expanded  upper  extremity,  the  head  or 
globus  major  (Figs.  225  and  226,  c) ;  a  middle  piece,  the  body  (Fig.  226, 
d) ;  and  a  shghtly  expanded  lower  extremity,  the  tail  or  globus  minor. 
From  the  last  named  passes  off  the  main  excretory  duct  of  the  testis, 
the  vas  deferens  (Fig.  225,  vd).     All  of  the  tubules  of  the  epididymis 

are  continuous  on  the  one 

e  a 

i         -   .„  hand  with  the  tubules  of 

the  testicle,  and  on  the 
other  with  the  vas  deferens. 
They  thus  constitute  a 
portion  of  the  complex  sys- 
tem of  excretory  ducts  of 
the  testicle. 

The  seminiferous 
tubule  may  be  divided 
with  reference  to  structure 
and  location  into  three 
parts,  (i)  A  much  convo- 
luted part,  the  convoluted 
tubule,  which  begins  at  the 
base  and  occupies  the 
greater  portion  of  a  lobule 
of  the  testis  (Fig.  229,  a). 
As  they  approach  the  apex 
of  a  lobule  several  of  these 
convoluted  tubules  unite  to 
form  (2)  the  straight  tubule 
(Fig.  225,  s,  229).  This 
passes  through  the  apex 
of  the  lobule  to  the  mediastinum,  where  it  unites  with  other  straight 
tubules  to  form  (3)  the  irregular  network  of  tubules  of  the  medias- 
tinum, the  rete  testis  (Fig.  229,  c). 

I.  The  Convoluted  Tubule. — This,  which  may  be  considered 
the  most  important  secreting  portion  of  the  lobule,  since  it  is  here 
that  the  spermatozoa  are  formed,  has  a  diameter  of  from  150  to  250/^. 
The  tubules  begin,  some  blindly,  others  by  anastomoses  with  neigh- 
boring tubules,  near  the  periphery  of  the  lobule,  and  pursue  a  tortuous 
course  toward  its  apex  (Fig.  229,  a). 

The  wall  of  the  convoluted  tubule  (Fig.  227)  consists  of  three 


.-— ^ 


Fig.  226. — Longitudinal  Section  through  Human 
Testis  and  Epididymis.  X2.  (Bohm  and  von 
Davidoff.)  The  Hght  strands  are  connective- 
tissue  septa,  a,  Tunica  albuginea;  h,  mediastinum 
and  rete  testis;  c,  head  of  epididymis;  d,  body  of 
epididymis;  e,  lobule;  s,  straight  tubules;  t,  vas 
epididymis. 


THE  REPRODUCTIVE  SYSTEM 


335 


layers:  (a)  An  outer  layer  composed  of  several  rows  of  flattened  con- 
nective-tissue cells  which  closely  invest  the  tubule;  (b)  a  thin  base- 
ment membrane;  and  (c)  a  lining  epithelium.  The  epithelium  con- 
sists of  two  kinds  of  cells,  the  so-called  supporting  or  sustentacular 
cells  and  the  glandular  cells  proper,  the  spermatogenic  cells. 

The  sustentacular  cells,  or  columns  of  Sertoli,  are  irregular,  high, 
epitheHal  structures,  whose  bases  rest  upon  the  basement  membrane, 


sf 


SC 


ijs 
sf  M 


Fig.  227. — Cross  Section  of  Convoluted  Portion  of  Human  Seminiferous  ".Tubule. 
X480.  (Kollikcr.)  M,  Basement  membrane;  i,  its  inner  homogeneous  layer;  fs,  its 
outer  fibrous  layer;  s,  nucleus  of  Sertoli  cell;  sp,  spermatogone;  sc,  spermatocyte;  sc' , 
spermatocyte  showing  mitosis;  ,s/,  nearly  mature  spermatozoon;  sf ,  spermatozoon  free 
in  lumen  of  tubule;  d,  degenerating  nucleus  in  lumen;/,  fat  droplets  stained  byi^osmic 
acid. 

and  which  extend  through  or  nearly  through  the  entire  epithelium 
(Fig.  228,  s).  Their  sides  show  marked  irregularities  and  depressions, 
due  to  the  pressure  of  surrounding  spermatogenic  cells.  Their  nuclei 
are  clear,  being  poor  in  chromatin  and  their  protoplasm  contains 
browni.sh  fat  droplets.  The  cells  of  Sertoli  have  long  been  considered 
as  sustentacular  in  character.  It  has  recently  been  suggested  that 
these  cells  are  derived  from  the  spermatogenic  cells,  but  that,  in- 
stead of  developing  into  spermatozoa, they  undergo  retrograde  changes. 


336  THE  ORGANS 

their  protoplasm  mingling  with-  the  intercellular  substance,  their 
nuclei  becoming  lost  and  the  cells  finally  disappearing.  According  to 
this  theory  the  tuft-like  arrangement  of  the  spermatozoa  about  the 
ends  of  the  Sertoli  cells  is  due  to  pressure  by  surrounding  spermato- 
genic  cells  (Figs.  228,  A  and  230,  /). 

h  s  b  h  f 

^       !  L^  ^/ 


/ 


r  * 


^   St 


sc  -- 


St.     — 


—    m 


/'yd 


'W0^^^  ■  i ''        "  ^P 


Fig.  228. — Parts  of  Transverse  Section  of  three  Seminiferous  Tubules  from  Testis  of 
White  Mouse.  X600.  (Szymonowicz.)  5,  SertoU  cell  with  nucleus;  i-^,  spermatogone, 
resting  state;  sp',  spermatogone  in  mitosis;  sc,  spermatocyte;  st,  spermatid;  sf,  spermatid 
developing  into  spermatozoon;  h,  head  of  spermatozoon;  /,  tails  of  developing  sper- 
matozoa; b,  blood-vessel;  c,  interstitial  cell;  m,  basal  membrane;/,  fat  droplets. 

The  appearance  which  the  spermatogenic  cells  present  depends 
upon  the  functional  condition  of  the  tubule.  In  the  resting  state  the 
epithelium  consists  of  several  layers  of  spherical  cells  containing 
nuclei  which  stain  with  varying  degrees  of  intensity.  In  the  active 
state  several  distinct  layers  of  spermatogenic  cells  can  be  differen- 
tiated.    These  from  without  inward  are  as  follows : 

(i)  Spermatogones  (Figs.  227  and  228,  sp). — These  are  small  cu- 
boidal  cells  which  he  against  the  basement  membrane.  Their  nuclei  are 
spherical  and  rich  in  chromatin.  By  mitotic  division  of  the  spermat- 
ogones are  formed  the  cells  of  the  second  layer,  the  spermatocytes. 


THE  REPRODUCTIVE  SYSTEM 


337 


(2)  Spermatocytes  (Figs.  227  and  228,  so). — These  are  larger  spher- 
ical cells  with  abundant  cytoplasm  and  large  vesicular  nuclei  showing 
various  stages  of  mitosis.  They  form  from  two  to  four  layers  to  the 
inner  side  of  the  spermatogones,  and  are 
sometimes  differentiated  into  spermat- 
ocytes of  the  first  order  and  spermato- 
cytes of  the  second  order.  By  mitotic 
division  of  the  innermost  spermatocytes  ^-^  -  - 
are  formed  the  spermatids. 

(3)  The  spermatids  (Figs.  227  and  228,  >o 
st)  are  small  round  cells  which  line  the  Q 


'D 


llG. 


230. 


Fig.  229.— Passage  of  Convoluted  Part  of  Seminiferous  Tubules  into  Straight  Tu- 
bules and  of  these  into  the  Rete  Testis  (Milhalicowicz.)  a,  Convoluted  part  of  tubule; 
b,    fibrous  stroma  continued  from  the  mediastinum  testis;  c,  rete  testis. 

Fig.  230. — Spermatoblast  with  some  Adjacent  Sperm  Cells,  from  Testis  of  Sparrow. 
(From  Kcilliker,  after  Etzold.)  M,  Basement  membrane;  s,  nucleus  of  SertoU  cell;  sp, 
spermatogones;  ic,  spermatocyte;  s^i  and  5/2,  spermatids  lying  along  the  surface  of 
the  Sertoli  cell,  s'  and  sh;  at  5/3  are  seen  the  nearly  mature  spermatozoa;  /,  tuft-like 
arrangement  of  bodies  of  spermatids  around  free  end  of  Sertoli  cell,  with  two  mature 
spermatozoa. 

lumen  of  the  seminiferous  tubule.     They  are  the  direct  progenitors  of 
the  spermatozoa.     (For  details  of  spermatogenesis  see  page  344.) 

In  the  actively  secreting  testicle  spermatozoa  are  frequently  found 

either  free  in  the  lumen  of  the  tubule  or  with  their  heads  among  the 

superficial  cells  and  their  tails  extending  out  into  the  lumen  (Figs. 

227,  sf  and  230).     There  are  also  found  in  the  lumen  many  small 

22 


338  THE  ORGANS 

cells  with  dark  nuclei.     These  are  spermatids  which  have  become  free 
and  which  degenerate  without  forming  spermatozoa. 

Separating  and  supporting  the  convoluted  tubules  is  a  small 
amount  of  interstitial  connective  tissue  in  which  are  the  blood-vessels 
and  nerves.     Among  the  usual  connective-tissue  elements  are  found 


c 


Fig.  231. — From  Section  through  Human  Mediastinum  and  Rete  Testis.  X96. 
(Kolliker.)  A,  Artery;  V,  vein;  L,  lymph  space;  C,  canals  of  rete  testis;  s,  cords  of  tis- 
sue projecting  into  the  lumina  of  the  tubviles  and  so  cut  transversely  or  obliquely;  Sk, 
section  of  convoluted  portion  of  seminiferous  tubule. 

groups  of  rather  large  spherical  cells  with  large  nuclei — interstitial 
cells.  They  are  believed  to  represent  remains  of  the  Wolffian  body 
(Fig.  228,  c). 

2.  The  Straight  Tubule  .---With  the  termination  of  the  con- 
voluted portion,  the  spermatogenic  tissue  of  the  gland  ends,  the 
remainder  of  the  tubule  constituting  a  complex  system  of  excretory 
ducts.     The  straight  tubule  is  much  narrower  than  the  convoluted, 


THE  REPRODUCTIVE  SYSTEM 


339 


having  a  diameter  of  from  20  to  z|o/<.     It  is  lined  by  a  single  layer  of 
cuboidal  cells  resting  upon  a  thin  basement  membrane.     At  the  apex 
of  the  lobule  the  straight  tu- 
bules become  continuous  with  ^■ 
the  tubules  of  the  rete  testis.       ^^  ' 

3.  The  Tubules  of  the 
Rete  Testis. — These  are  ir- 
regular canals  which  vary 
greatly  in  shape  and  size. 
They  are  lined  with  a  single 
layer  of  low  cuboidal  or  fiat 
epithehal  cells  (Fig.  231,  C). 

The  Seminal  Ducts. — While 
the  already  described  straight 

tubules  and  the  tubules  of  the  rete  testis  must  be  regarded  as  part  of 
the  complex  excretory  duct  system  of  the  testis,  there  are  certain 
structures  which  are  w'holly  outside  the  testis  proper,  which  serve  to 
transmit  the  secretion  of  the  testis,  and  are  known  as  the  seminal 
ducts.     On  leaving  the  testis  these  ducts  form  the  epididymis,  after 


Fig.  232. — Part  of  a  Cross  Section  through 
a  Vas  Efferens  of  the  Human  P^pididymis. 
X140.  (KoUiker.)  F,  High  columnar  cifiated 
epithelium;  d,  lower  non-ciliated  epithelium, 
presenting  appearance  of  a  gland;  d' ,  the  same 
cut  obliquely. 


m 


'  ■^.i'^^%  /'/,■'         -'-^^  c  ■'';",,',"-  ■■ 

m 
Fig.   233. — From  Cross  Section  through  Head  of  E|)ididymis.      y.Z'^.     (KoUiker.) 
6,  Interstitial  connective  tissue;  c  sections  through  tubules  of  epididymis,  showing  two- 
layered  columnar  epithelium;  g,  blood-vessel. 

which  they  converge  to  form  the  main  excretory  duct  of  the  testis, 
the  vas  deferens. 

The  Epididymis. — From  the  tubules  of  the  rete  testis  arise  from 
eight  to  fifteen  tubules,  the  vasa  eferenlia,  or  efferent  ducts  of  the 


340  THE  ORGANS 

testis  (Fig.  225,  e).  Eacli  vas  effexens  piusnes  a  tortuous  course,  is 
separated  from  its  fellows  by  connective  tissue,  and  forms  one  of  the 
lobules  of  the  bead  of  tbe  epidid3Tnis.  The  epithelium  of  the  ^^asa 
efferentia  consists  of  two  kinds  of  cells,  high  columnar  cihated  cells 
(Fig.  232,  F),  and,  interspersed  among  these,  low  cuboidal  non- 
ciliated  cells  (Fig.  232,  d).  Occasionall}'  some  of  the  high  ceOs  are 
free  from  ciha  and  some  of  the  cuboidal  cells  ma3"  bear  dlia.  The 
cuboidal  cells  he  in  groups  between  groups  of  the  higher  cells,  often 

giAing  the  appearance  of  ciypt- 
I  ■  .  ''}\  \  h  like    depressions.       Th^e   liave 

*'''^*=-~----===^_^________^^    ...:>--' — ''        been  referred  to  as  intraepithelial 

■'  :=:,,;:^ glands.     The}'  do  not,  howeveTj 

I  ■  '       .   ,     ;!     '   K3  invaginate  the  underlying  tissues. 

The  epithehum  rests  upon  a  base- 
ment membrane,  beneath  which 
are  several  layers  of  circularly 
disposed  smooth  musde  ceis. 
The  vasa  efferentia  converge  to 
""         form  the  i^as  epididymis  (Fig.  233). 

Waiwl-  ¥4^e''of"Epid!SS".  "^xt.     ^ere    the    epitheli™  is  "of  the 

(Xolliker.)    (Fig.  233  more  highly  magni-     stratified  "^^uriety,  there  being  two 

fied.)      &,  Connective-tissue  and  smooth                ,                           r      n  tt'Tl. 

musde  cells;  r,  basal  layer  of  epithehal  O^    three  rowS  Ol  celis.  Ihe  SW~ 

^eUs;  /,  high  columaiar  epithelial  cells;  p,  f^^g   ^g^g   ^^^   narrow,  high,  and 

pigment  granules  m  columnar   cells;    r.         _  _                                     .  . 

cuticula;  /?,  ciha.  cihated,     and    their    nuclei    are 

placed  at  different  levels  (Fig. 
234).  The  ciha  are  long  and  each  ceU  has  onl}'  a  few  cilia.  The 
deeper  cells  are  irregular  in  shape.  The  basement  membrane  and 
muscular  layers  are  the  same  as  in  the  vasa  efferentia.  As  the  vas 
deferens  is  approached  the  muscular  coat  becomes  thickened,  and 
is  sometimes  strengthened  by  the  addition  of  scattered  bundles  of 
longitudinal^  disposed  cells. 

The  Vas  Deferens. — The  walls  of  the  vas  deferens  consist  of 
four  coats — mucosa,  sub  mucosa,  muscularis,  and  fibrosa  (Fig.  235), 

The  mucosa  is  folded  longitudinall}',  and  is  composed  of  a  stroma 
and  a  lining  epithehum.  The  epithehum  is  of  the  stratified  columnar 
type  with  two  or  three  rows  of  cells,  being  similar  to  that  lining  the 
vas  epididymis.  The  extent  to  which  the  epithelium  is  cihated 
varies  greatly.  In  some  cases  the  entire  vas  is  cihated,  in  others  only 
the  upper  portion,  in  still  others  no  ciha  are  present  bej^ond  the  epi- 
did3'mis.     The  epithehum  rests  upon  a  basement  membrane  beneath 


THE  REPRODUCTIVE  SYSTEM  341 

which  is  a  libro-elastic  cellular  stroma.     The  stroma  merges  without 
distinct  demarcation  into  the  more  vascular  subniucosa. 

The  ninscularis  consists  of  two  strongly  developed  layers  of  smooth 
muscle,  an  inner  circular  and  an  outer  longitudinal  (Fig.  235),  which 
together  constitute  about  seven-eighths  of  the  wall  of  the  vas.  At 
the  beginning  of  the  vas  deferens  a  third  layer  of  muscle  is  added 
composed  of  longitudinal  bundles,  and  situated  between  the  inner 
circular  laver  and  the  submucosa. 


■•-,w:-'  -  -    C 


Fig.  235. — Cross  Section  of  Human  Vas  Deferens.  X37.  (Szymonowicz.)  a, 
Epithelium;  b,  stroma;  c,  submucosa;  d,  inner  circular  muscle  layer;  e,  outer  longitudinal 
muscle  layer;  /,  fibrous  layer;  g,  blood-vessels. 

The  fibrosa  consists  of  fibrous  tissue  containing  many  elastic 
fibres. 

Near  its  termination  the  vas  dilates  to  form  the  ampulla,  the 
walls  of  which  present  essentially  the  same  structure  as  those  of  the 
vas.  The  lining  epithelium  is,  however,  frequently  markedly  pig- 
mented and  the  mucosa  ccjntains  branched  tubular  glands. 

The  Seminal  Vesicles  and  Ejaculatory  Ducts.^ — The  seminal 
vesicles.  The  walls  of  the  seminal  vesicles  are  similar  in  structure  to 
those  of  the  ampulla.  The  epithelium  is  pseudo-stratified  with  two 
or  three  rows  of  nuclei  and  contains  a  yellow  pigment.  When  the 
vesicles  are  distended  the  epithelium  flattens  out  and  the  nuclei  lie 
more  in  one  plane,  thus  giving  the  appearance  of  an  ordinary  simple 


342  THE  ORGANS 

columnar  epithelium.  Beneath  the  epithelium  is  a  thin  stroma,  out- 
side of  which  is  an  inner  circular  and  an  outer  longitudinal  layer  of 
smooth  muscle,  both  layers  being  much  less  developed  than  in  the 
vas.  The  seminal  vesicles  are  to  be  regarded  as  accessory  genital 
glands. 

The  ejaciilatory  ducts  are  lined  with  a  single  layer  of  columnar 
cells.  The  muscularis  is  the  same  as  in  the  ampulla  except  that  the 
inner  circular  layer  is  thinner.  In  the  prostatic  portion  of  the  duct 
the  muscularis  is  indistinct,  merging  with  the  muscle  tissue  of  the 
gland.  The  ducts  empty  either  directly  into  the  urethra  or  into  the 
urethra  through  the  vesicula  prostatica. 

Rudimentary  Structtires  Connected  with  the  Development  of  the  Genital 
System. — Connected  with  the  testicle  and  its  ducts  are  remains  of  certain 
fcEtal  structures.     These  are: 

(i)  The  paradidymis,  or  organ  of  Gir aides,  situated  between  the  vessels  of 
the  spermatic  cord  near  the  testis.  It  consists  of  several  blind  tubules  lined 
with  simple  columnar  ciliated  epithelium. 

(2)  The  ductus  aberraus  Halleri,  found  in  the  epididymis.  It  is  lined  with 
simple  columnar  ciliated  epithelium  and  opens  into  the  vas  epididymis.  In- 
stead of  a  single  ductus  aberrans,  several  ducts  may  be  present. 

(3)  The  appendix  testis  (stalked  hydatid  or  hydatid  of  Morgagni),  in  the 
upper  part  of  the  globus  major.  It  consists  of  a  vascular  connective  tissue 
surrounding  a  cavity  lined  with  simple  columnar  ciliated  epithelium. 

(4)  The  appendix  epididymidis,  a  vascular  structure,  not  always  present, 
lying  near  the  appendix  testis.     It  resembles  the  latter  in  structure. 

The  paradidymis  and  ductus  aberrans  Halleri  probably  represent  remains 
of  the  embryonal  mesonephros.  The  appendix  testis  and  the  appendix  epididy- 
midis are  believed  by  some  to  be  derived  from  the  primitive  kidney,  by  others 
from  the  embryonal  duct  of  jNIiiller. 

Blood-vessels. — Branches  of  the  spermatic  artery  ramify  in  the 
mediastinum  and  in  the  tunica  vasculosa.  These  send  branches  into 
the  septa  of  the  testicle,  which  give  rise  to  a  capillary  network  among 
the  convoluted  tubules.  From  the  capillaries  arise  veins  which 
accompany  the  arteries. 

L5miph  capillaries  begin  as  clefts  in  the  tunica  albuginea  and  in 
the  connective  tissue  surrounding  the  seminiferous  tubules.  These 
connect  with  the  more  definite  lymph  vessels  of  the  mediastinum  and 
of  the  spermatic  cord. 

Nerves. — Non-meduUated  nerve  fibres  form  plexuses  around  the 
blood-vessels.  From  these,  fibres  pass  to  plexuses  among  the  semi- 
niferous tubules.  Their  exact  method  of  termination  in  connection 
mth  the  epithelium  has  not  been  determined.     In  the  epididymis 


THE  REPRODUCTIVE  SYSTEM 


343 


Head 


Anterior  end  knob 
Posterior  end  knob 


are  found  small  sympathetic  ganglia.  The  walls  of  the  vasa  effer 
entia,  vas  epididymis,  and  vas  deferens  contain  plexuses  of  non-medul- 
lated  nerve  fibres,  which  give  off 
terminals  to  the  smooth  muscle 
cells  and  to  the  mucosa. 

The  Spermatozoa.  —  The 
spermatozoa  are  the  specific  secre- 
tion of  the  testicle.  Human 
spermatozoa  are  long,  slender 
flagellate  bodies,  from  50  to  70/f 
in  length,  and  are  suspended  in 
the  semen,  which  is  a  secretion  of 
the  accessory  sexual  glands.  The 
general  shape  is  that  of  a  tadpole; 
and  by  means  of  an  undulatory 
motion  of  the  tail,  the  spermato- 
zoon is  capable  of  swimming  about 
freely  in  a  suitable  medium.  It 
has  been  estimated  that  the  human 
spermatozoa  average  about  sixty 
thousand  per  cubic  millimetre  of 
semen. 

The  human  spermatozoon  con- 
sists of  (i)  a  head,  (2)  a  middle 
piece  or  body,  and  (3)  a  tail  or 
flagellum  (Fig.  236). 

The  head,  from  3  to  5/«  long  and 
about  half  that  in  breadth,  is  oval 
in  shape  when  seen  on  flat,  pear- 
shaped  when  seen  on  edge.  It 
consists  mainly  of  chromatin  de- 
rived from  the  nucleus  of  the 
parent  cell.  Enveloping  the  nu- 
clear material  of  the  head  is  a  thin 
layer  or  delicate  membrane  of  cyto- 
plasm, the  galea  capitis.  The 
front  of  the  head  ends  in  a  sharp  edge,  the  apical  body  or  acrosome. 
In  some  lower  forms  the  acrosome  is  much  more  highly  developed 
than  in  man  and  extends  forward  as  a  pointed  or  barbed  spear,  the 
perjoralorium.      The  acrosome   is  differentiated   from  the  nuclear 


Main  segment 
of  tail 


Fig.  236. — Diagram  of  a  Human  Sper- 
matozoon.    (Meves,  Bonnet.) 


344  THE  ORGANS 

portion  of  the  head  by  taking  an  acid  dye,  the  chromatin,  of  course, 
taking  a  basic  stain. 

The  body  is  cyHndrical,  about  the  same  length  as  the  head,  and 
consists  of  a  iibrillated  central  core,  the  axial  thread,  surrounded  by 
a  protoplasmic  capsule.  A  short  clear  portion,  the  neck,  unites  the 
head  and  body.  Just  behind  the  head  the  axial  thread  presents  a 
bulbous  thickening,  the  anterior  end  knob,  which  fits  into  a  depression 
in  the  head.  At  the  junction  of  neck  and  body  are  one  or  several 
posterior  end  knobs  to  which  the  axial  thread  is  attached.  The 
latter  leaves  the  body  through  a  perforated  ring,  the  end  ring  or  end 
disc.  Delicate  fibrils — spiral  fibres — run  spirally  around  the  body 
portion  of  the  axial  thread. 

The  tail  consists  of  a  main  segment,  from  40  to  6o,«  in  length,  and 
a  terminal  segment  having  a  length  of  from  5  to  io;<.  The  main  seg- 
ment has  a  central  iibrillated  axial  thread  which  is  continuous  with 
the  axial  thread  of  the  body.  This  is  enclosed  in  a  thin  cytoplasmic 
membrane  or  capsule  continuous  with  the  capsule  of  the  body.  This 
membrane,  inconspicuous  and  apparently  structureless  in  man,  is 
remarkably  developed  in  some  lower  forms,  e.g.,  the  membrana 
undulata  of  birds.  The  terminal  segment  consists  of  the  axial  thread 
alone.  The  motility  of  the  spermatozoon  depends  entirely  upon  the 
flagellate  movements  of  the  tail.  In  many  of  the  lower  animals  the 
spermatozoon  has  a  much  more  complicated  structure. 

Of  the  above-described  parts  of  the  spermatozoon  only  the  head  and 
tail  can  usually  be  differentiated,  except  by  the  use  of  special  methods  and 
very  high-power  objectives. 

Development  of  the  Spermatozoa. — As  already  noted  in  describing  the 
testicle,  the  spermatozoa  are  developed  from  the  epithelial  ceUs  of  the  semi- 
niferous tubules.  The  most  peripheral  of  the  tubule  cells,  the  spermatogones 
(Fig.  227,  sp  and  Fig.  228,  sp)  are  small  round  cells  with  nuclei  rich  in  chromatin. 
By  mitosis  the  spermatogone  gives  rise  to  two  daughter  cells,  one  of  which 
remains  at  the  periphery  as  a  spermatogone,  while  the  other  takes  up  a  more 
central  position  as  a  spermatocyte  (Fig.  228,  sc  and  Fig.  230,  sc).  The  latter  are 
rather  large  spherical  cells,  whose  nuclei  show  very  distinct  chromatin  networks. 
By  mitotic  division  of  the  spermatocytes  of  the  innermost  row  are  formed  the 
spermatids  (Fig.  228,  st  and  Fig.  230,  st).  These  are  small  spherical  cells,  which 
line  the  lumen  of  the  tubule  and  are  the  direct  progenitors  of  thu  spermatozoa. 
In  the  transformation  of  spermatocyte  into  spermatid  an  extremely  important 
change  takes  place  in  the  nucleus.  This  consists  in  a  reduction  of  its  chromosomes 
to  one-half  the  number  specific  for  the  species  (page  58) .  The  transformation  of 
the  spermatid  into  the  spermatozoon  differs  somewhat  in  different  animals  and 
the  details  of  the  processmust  be  regarded  as  not  yet  definitely  determined.     The 


THE  REPRODUCTIVE  SYSTEM 


345 


nucleus  of  the  spermatid  first  becomes  oval  in  shape,  and  its  chromosomes  be- 
come condensed  into  a  small  homogeneous  mass,  which  forms  the  head  of  the 
spermatozoon.  During  their  transformation  into  the  heads  of  the  spermatozoa, 
the  nuclei  of  the  spermatids  arrange  themselves  in  tufts  against  the  inner  ends 
of  the  cells  of  Sertoli.  This  compound  structure,  consisting  of  a  Sertoli  cell 
and  of  a  group  of  developing  spermatozoa  attached  to  its  central  end,  is  known  as 
a  spermatoblast  (Fig.  230).  The  body  or  middle  piece  of  the  spermatozoon  is 
described  by  most  investigators  as  derived  from  the  centrosome,  while  the  tail 
is  a  derivative  of  the  cytoplasm. 


Head 


Anterior  end  knob 
Posterior  end  knob 


Head 


Anterior  end  knob 
Posterior  end  knob 


End  ring 


Nucleus 


Cytoplasm 


.:—  Proximal  centrosome 

7 


Distal  centrosone 


Fig.  237. — Transformation  of  a  Spermatid  into  a  Siiermatozoon  (human).     Schematic 

(Meves,  Bonnet.) 


The  details  of  the  transformation  of  the  spermatid  into  the  spermatozoon  are 
illustrated  in  Fig.  237.  The  centrosome  either  divides  completely,  forming  two 
centrosomes,  or  incompletely,  forming  a  dumb-bell-shaped  body.  The  nuclear 
material  becomes  very  compact  ancl  passes  to  one  end  of  the  cell,  forming  the 
bulk  of  the  head.  Both  centrosomes  help  to  form  the  body.  They  first  become 
disc-shaped.  'J'he  one  lying  nearer  the  centre  of  the  cell  becomes  attached  to  the 
posterior  end  of  the  head  as  the  anterior  end-knob,  the  other  takes  a  position  a 


346  THE  ORGANS 

little  more  posteriorly  as  the  posterior  end-knob  and  from  it  grows  out  the  axial 
filament.  Some  of  this  centrosome  passes  to  the  posterior  limits  of  the  body 
and  there  becomes  the  end  ring.  As  the  two  parts  of  this  centrosome  separate 
the  delicate  cytoplasm  between  them  forms  the  spiral  fibres.  During  these 
changes  the  axial  filament  has  been  growing  and  projects  beyond  the  limits  of 
the  cell.  Most  of  the  cytoplasm  of  the  spermatid  is  not  used  in  the  formation 
of  the  spermatozoon,  but  is  cast  off  and  degenerates.  A  small  amount  is  used 
for  the  sheath  of  the  body,  and  for  the  galea  capitis.  The  sheath  of  the  main 
part  of  the  filament  appears  to  develop  from  the  filament  itself. 

The  significance  of  the  different  parts  of  the  spermatozoon  has  been  brought 
out  in  describing  its  development.  From  this  it  is  seen  that  the  spermatozoon, 
like  the  mature  ovum,  is  a  true  sexual  element  with  one-half  the  somatic  number 
of  chromosomes.  The  head  and  body,  containing  the  chromatin  and  the  centro- 
somes,  are  the  parts  of  the  spermatozoon  essential  to  fertilization.  The  acro- 
some  is  an  accessory  which  in  some  forms  at  least  aids  the  spermatozoon  in 
attaching  itself  to  and  in  entering  the  ovum.  The  tail  is  an  accessory  structure 
which  provides  motion,  enabhng  the  spermatozoon  to  move  about  freely  in  the 
semen  and  in  the  fluids  of  the  female  generative  tract.  Considering  their 
minuteness,  their  speed  is  considerable,  having  been  estimated  at  from  1.5  to 
3.5  mm.  per  minute;  enough  to  allow  them  to  ascend  through  uterus  and  oviduct 
against  the  adverse  action  of  the  cilia.  When  in  a  favorable  environment, 
such  as  the  fluids  of  the  female  generative  tract,  the  spermatozoon  is  capable 
of  living  for  some  time  after  leaving  the  testicle.  Living  spermatozoa  have  been 
found  in  the  uterus  or  tubes  three  and  a  half  weeks  after  coitus. 


TECHNIC 

(i)  For  the  study  of  the  general  topography  of  the  testis,  remove  the  testis  of 
a  new-born  child,  make  a  deep  incision  through  the  tunica  albuginea  in  order  to 
allow  the  fixative  to  penetrate  quickly,  and  fix  in  formahn-M tiller's  fluid  (technic 
5,  p.  7).  Antero-posterior  longitudinal  sections  through  the  entire  organ  and  in- 
cluding the  epididymis  should  be  stained  with  hsematoxylin-picro-acid-fuchsin 
(technic  3,  p.  21)  or  with  haematoxylin-eosin  (technic  i,  p.  20)  and  mounted  in 
balsam. 

(2)  The  testis  of  a  young  adult  is  removed  as  soon  after  death  as  possible,  is 
cut  into  thin  transverse  shces,  which  include  the  epididymis,  and  is  fixed  in  forma- 
lin-Miiller's  or  in  Zenker's  fluid  (technic  9,  p.  8).  Select  a  slice  which  includes 
the  head  of  the  epididymis,  cut  away  the  anterior  half  or  two-thirds  of  the  testis 
proper  in  order  to  reduce  the  size  of  the  block,  and,  after  the  usual  hardening 
and  embedding,  cut  thin  sections  through  the  remaining  posterior  portion  of 
the  testis,  the  mediastinum,  and  epididymis.  Stain  with  haematoxyhn-eosin 
(technic  i,  p.  20)  and  mount  in  balsam. 

(3)  For  the  study  of  spermatogenesis  fix  a  mouse's  testis  in  chrome-acetic- 
osmic  mixture  (technic  7,  p.  7).  Harden  in  alcohol  and  mount  thin  unstained 
sections  in  balsam  or  in  glycerin. 

(4)  Spermatozoa. — -Human  spermatozoa  may  be  examined  fresh  in  warm 
normal  sahne  solution  or  fixed  in  saturated  aqueous  solution  of  picric  acid  and 


THE  REPRODUCTIVE  SYSTE:\I  347 

mounted  in  glycerin.  ^lammalian  spermatozoa  may  be  obtained  from  the 
vagina  after  intercourse,  or  by  incision  into  the  head  of  the  epididymis.  Technic 
same  as  for  human. 

(5)  A  portion  of  the  vas  deferens  is  usually  removed  with  the  testis  and  may 
be  subjected  to  technic  (2)  above.  Transverse  sections  are  stained  with  haema- 
toxylin-eosin  and  mounted  in  balsam. 

The  Prostate  Gland 

The  prostate  is  described  by  some  as  a  compound  tubular,  by 
others  as  a  compound  alveolar  gland.  It  is  perhaps  best  regarded 
as  a  collection  of  simple  branched  tubular  glands  with  dilated  termi- 
nal tubules.     These  number  from  forty  to  fifty,  and  their  ducts  con- 


"---W 


■* , 


/■  -•'■::^''-^ '  "'^  -V 'V 't:\    '^""'^'^^'% 


h  -■■-"' "  \ 


* . 


FiG.  238. — Section  of  Human  Prostate.     X150.     (Technici,p.  349.)     a,  Epithelium  of 
lubule;  h,  interstitial  connective  tissue;  c,  corpora  amylacea. 

verge  to  form  about  twenty  main  ducts,  which  open  into  the  urethra. 
The  gland  is  surrounded  by  a  capsule  of  fibro-elastic  tissue  and  smooth 
muscle  cells,  the  muscle  cells  predominating.  From  the  capsule 
broad  trabeculce  of  the  same  structure  as  the  capsule  pass  into  the 
gland.  The  amount  of  connective  tissue  is  large.  It  is  less  in  the 
prostate  of  the  young  than  of  the  old.  The  hypertrophied  prostate 
of  age  is  due  mainly  to  an  increase  in  the  connective-tissue  elements. 
The  tubules  have  wide  lumina  and  are  lined  with  simple  cuboidal 
epithelium  of  the  serous  type,  resting  upon  a  delicate  basement  mem- 


348  THE  ORGANS 

brane  (Fig.  238).  Less  commonly  the  epithelium  is  pseudo-strati- 
fied.  The  ducts  are  lined  with  simple  columnar  epithelium  until 
near  their  terminations  where  they  are  hned  with  transitional  epithe- 
lium similar  to  that  lining  the  urethra.  Peculiar  concentrically 
laminated  bodies,  crescentic  corpuscles,  or  corpora  amylacea,  are  fre- 
quently present  in  the  terminal  tubules  (Fig.  238,  c).  They  are 
more  numerous  after  middle  life.  Through  the  prostate  runs  the 
prostatic  portion  of  the  urethra. 

Within  the  prostate  is  found  the  vesicula  prostatica  {utriculus 
prostaticus — uterus  masculinus).  It  represents  the  remains  of  a 
foetal  structure,  the  Mullerian  duct  and  consists  of  a  blind  sac  with 
folded  mucous  membrane  lined  with  a  two-rowed  ciliated  epithelium 
which  dips  down  to  form  short  tubular  glands.  The  prostatic  secre- 
tion is  serous. 

The  blood-vessels  of  the  prostate  ramify  in  the  capsule  and  tra- 
beculse.  The  small  arteries  give  rise  to  a  capillary  network  which 
surrounds  the  gland  tubules.  From  these  arise  small  veins,  which 
accompany  the  arteries  in  the  septa  and  unite  to  form  venous  plexuses 
in  the  capsule. 

The  lymphatics  begin  as  blind  clefts  in  the  trabeculae  and  fol- 
low the  general  course  of  the  blood-vessels. 

Nerves. — Small  groups  of  sympathetic  ganglion  cells  are  found  in 
the  larger  trabeculae  and  beneath  the  capsule.  Axones  of  these  cells 
pass  to  the  smooth  muscle  of  the  trabeculae  and  of  the  walls  of  the 
blood-vessels.  Their  mode  of  termination  is  not  known.  Timofeew 
describes  afferent  medullated  fibres  ending  within  capsular  structures 
of  fiat  nucleated  cells.  Two  kinds  of  fibres  pass  to  each  capsule: 
one  a  large  medullated  fibre  which  loses  its  sheath  and  gives  rise 
within  the  capsule  to  several  flat  fibres  with  serrated  edges,  the  other 
small  medullated  fibres  which  lose  their  sheaths  and  split  up  into 
small  varicose  fibrils  which  form  a  network  around  the  terminals  of 
the  large  fibre. 

Cowper's  Glands 

The  bulbo-urethral  glands,  or  glands  of  Cowper,  are  small,  com- 
pound tubular  glands.  Both  tubules  and  ducts  are  irregular  in  diam- 
eter so  that  some  of  them  have  more  the  character  of  alveoli  than 
of  tubules.  They  are  lined  with  mucous  cells.  The  smaller  ducts  are 
lined  with  simple  cuboidal  epithelium.     They  unite  to  form  two  main 


THE  REPRODUCTIVE  SYSTEM 


349 


excretory  ducts  which  open  into  the  urethra  and  are  lined  with 
stratified  columnar  epithelium  consisting  of  two  or  three  layers  of  cells. 
In  the  main  duct,  as  well  as  in  its  branches,  smooth  muscle  occurs. 

TECHNIC 

(i)  Fix  small  pieces  of  the  prostate  of  a  young  man  in  formalin-Miiller's  fluid 
(technic  5,  p.  7).  Stain  sections  with  haematoxylin-eosin  (technic  i,  p.  20)  and 
mount  in  balsam. 

(2)  The  prostate  of  an  old  man  should  be  treated  with  the  same  technic  and 
compared  with  the  above. 

(3)  Cowper's  glands.     Same  technic  as  prostate  (i). 


The  Penis 

The  penis  consists  largely  of  three  long  cylindrical  bodies,  the 
corpus  spongiosum  and  the  two  corpora  cavernosa.  The  latter  lie 
side  by  side,  dorsally,  while  the  corpus  spongiosum  occupies  a  medial 
ventral  position  (Fig.  239).  All  three  are  enclosed  in  a  common 
connective-tissue  capsule  which  , 

is  loosely  attached  to  the  over- 
lying skin.  In  addition  each 
corpus  has  its  own  special  cap- 
sule or  tunica  albuginea,  about 
a  millimetre  in  thickness,  and 
composed  of  dense  connective 
tissue  containing  many  elastic 
fibres. 

The  corpus  spongiosum  and 
corpora  cavernosa  have  essen- 
tially the  same  structure,  being 
composed  of  so-called  erectile 
tissue  (Fig.  240).  This  consists 
of  thick  trabeculae  of  inter- 
mingled fibro-elastic  tissue  and 

bundles  of  smooth  muscle  cells,  which  anastomose  to  form  a  coarse 
meshed  network,  the  spaces  of  which  are  lined  with  endothelium. 
The  spaces  are  known  as  cavernous  sinuses,  and  communicate 
with  one  another,  and  with  the  blood-vessels  of  the  penis.  In  the 
flaccid  condition  of  the  organ  these  sinuses  are  empty  and  their 
sides  are  in  apposition.  In  erection  these  sinuses  become  filled  with 
venous  Ijlood. 


I-'iG.  239. — Tran.-.\  i-r.-.c  Section  through 
Human  Penis.  a,  Skin;  b,  subcutaneous 
tissue;  c,  fibrous  tunic;  d,  dorsal  vein;  e, 
corpora  cavernosa;  /,  corpus  spongiosum; 
g,  urethra. 


350  THE  ORGANS 

The  arteries  have  thick  muscular  walls  and  run  in  the  septa.  A 
few  of  them  open  directly  into  the  venous  sinuses.  Most  of  them 
give  rise  to  a  superficial  capillary  network  beneath  the  tunica  albu- 
ginea.  From  this  capillary  plexus  the  blood  passes  into  a  plexus  of 
broader  venous  channels  in  the  periphery  of  the  erectile  tissue,  and 
these  in  turn  communicate  with  the  cavernous  sinuses.  The  usual 
direct  anastomoses  between  arterial  and  venous  capillaries  also  occur. 
The  blood  may  therefore  pass  either  through  the  usual  course— arte- 
ries, capillaries,  veins — or,  under  certain  conditions,  may  jpass  through 
the  cavernous  sinuses.  This  determines  the  flaccid  or  the  erect  con- 
dition of  the  organ.     The  veins  arise  partly  from  the  capillaries  and 


^''    ■-■■.'       .':■.•■';'.'■■■'  ,■    Z-:^"-      .   \     \  --^  >    h 


Fig.  240. — Erectile  Tissue  of  Corpus  Spongiosum  of  Human  Penis.  X60.  a, 
Trabeculse  of  connective  tissue  and  smooth  muscle;  b,  cavernous  sinuses;  c,  groups  of 
leucocytes  in  sinus. 

partly  from  the  cavernous  sinuses.  They  pass  through  the  tunica 
albuginea  and  empty  into  the  dorsal  vein  of  the  penis  (Fig.  239).  In 
the  corpus  spongiosum  there  is  probably  no  direct  opening  of  arteries 
into  sinuses.     Both  trabeculae  and  sinuses  are  also  smaller. 

Of  the  lymphatics  of  the  penis  little  definite  is  known. 

The  nerve  endings,  according  to  Dogiel,  consist  of:  (a)  free  sensory 
endings,  (b)  deeply  situated  genital  corpuscles,  (c)  Pacinian  corpus- 
cles and  Krause's  end-bulbs  in  the  more  superficial  connective  tissue, 
and  (d)  Meissner's  corpuscles  in  the  papillae;.  (For  details  see  pages 
432  and  433.) 

The  glans  penis  consists  of  erectile  tissue  similar  in  structure  to 


THE  REPRODUCTIVE  SYSTEM 


351 


that  of  the  corpus  cavernosum,  except  that  the  venous  spaces  are 
smaller  and  more  regular.  The  mucous  membrane  is  very  closely 
attached  to  the  fibrous  sheath  of  the 
underlying  erectile  tissue.  A  few 
small  sebaceous  glands,  unconnected 
with  hairs — the  glands  of  Tyson — 
are  found  in  the  mucous  membrane 
of  the  base  of  the  glans  penis. 

The  prepuce  is  a  fold  of  skin 
which  overlies  the  glans  penis.  Its 
inner  surface  is  lined  with  mucous 
membrane. 


Fig.  241.  Fig.  242. 

Fig.  241. — From  Transverse  Section  of  Urethra  and  Corpus  Spongiosum,  including 
Mucous  Membrane  and  part  of  Submucosa.  X15.  The  dark  spots  represent  the 
cavernous  veins. 

Fig.  242. — Vertical  Section  through  Portion  of  Wall  of  Human  Male  Urethra. 
X350.  A,  Mucous  membrane;  B,  submucosa;  a,  epithelium;  b,  stroma;  c,  cavernous 
veins;  d,  connective  tissue  of  submucosa. 


The  Urethral 

The  MALE  URETHRA  Is  divided  into  three  parts — prostatic,  mem- 
branous, and  penile.  The  wall  of  the  urethra  consists  of  three  coats — 
mucous,  submuccjus,  and  muscular.  The  structure  of  the  wall  differs 
in  the  different  parts  of  the  urethra. 

'J"he  mucous  membrane  (Fig.  242)  consists  of  epithelium  and 
stroma.     The  epithelium  of  the  prostatic  part  is  stratified  squamous 

*  The  female  urethra,  while  not  so  distinctly  divisible  into  sections,  presents  essen- 
tially the  same  structure  as  the  male  urethra.  The  epithelium  begins  at  the  bladder 
as  stratified  squamous  of  the  transitional  ty|)e,  changes  to  a  two-layered  stratified  or 
pscudostratified,  and  finally  jiasses  over  into  stratified  stjuamous  near  the  uretiiral 
opening.     Glands  of  Eittr6  are  jirescnt,  but  are  fewer  than  in  the  male. 


352  THE  ORGANS 

(transitional),  resembling  that  of  the  bladder.  In  the  membranous 
part  it  is  stratified  columnar  or  pseudostratified.  In  the  penile 
portion  it  is  pseudostratified  up  to  the  fossa  navicularis,  where  it 
changes  to  stratified  squamous.  The  epithelium  rests  upon  a  base- 
ment membrane,  beneath  which  is  a  thin  stroma  rich  in  elastic  fibres 
and  having  papillae  which  are  especially  prominent  in  the  terminal 
dilated  portion  of  the  urethra,  the  fossa  navicularis.  The  stroma 
merges  without  distinct  demarcation  into  the  submucosa. 

The  submucosa  consists  of  connective  tissue  and,  in  the  penile 
portion,  of  more  or  less  longitudinally  disposed  smooth  muscle.  It 
contains  a  dense  network  of  veins — cavernous  veins — which  give  it 
the  character  of  erectile  tissue  (Fig.  242). 

The  muscular  coat  is  thickest  in  the  prostatic  and  membranous 
portions.  Here  it  consists  of  a  thin  inner  longitudinal  and  a  thicker 
outer  circular  layer.  A  definite  muscular  wall  ceases  at  the  beginning 
of  the  penile  portion,  although  circularly  disposed  smooth  muscle 
cells  are  found  in  the  outer  part  of  the  submucosa  of  the  penile 
urethra. 

Throughout  the  mucosa  of  the  entire  urethra,  but  most  numerous 
in  the  penile  portion,  are  simple  branched  tubular  mucous  glands, 
the  glands  of  Littre.  They  are  lined  with  columnar  epithelium  and 
the  longer  extend  into  the  submucosa. 

TECHNIC 

(i)  For  the  study  of  the  general  topography  of  the  penis,  remove  the  skin 
from  the  organ  and  cut  into  transverse  slices  about  0.5  cm.  in  thickness.  Fix  in 
formalin-Mxiller's  fluid  (technic  5,  p.  7),  cut  rather  thick  sections  across  the 
entire  penis,  stain  with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  21)  or  with 
haematoxyhn-eosin  (technic  i,  p.  20)  and  mount  in  balsam. 

(2)  For  the  study  of  the  structure  of  the  penile  portion  of  the  urethra  and  of 
the  erectile  tissue  of  the  corpus  spongiosum,  cut  away  the  corpora  cavernosa, 
leaving  only  the  corpus  spongiosum  and  contained  urethra,  and  treat  as  above. 
Sections  should  be  thin  and  stained  with  haematoxylin-eosin. 

(3)  The  same  technic  is  to  be  used  for  the  membranous  and  prostatic 
portions  of  the  urethra. 

n.  FEMALE  ORGANS 
The  Ovary 

The  ovary  is  classed  as  one  of  the  ductless  glands.  Its  specific 
secretion  is  the  ovum.     The  ovary  has  no  duct  system  which  is 


THE  REPRODUCTIVE  SYSTEM 


353 


directly  continuous  with  its  structure.  In  place  of  this  it  is  provided 
with  what  may  be  considered  to  be  a  highly  specialized  disconnected 
excretory  duct — the  oviduct  or  Fallopian  tube — which  serves  for  the 
transmission  of  its  secretion  to  the  uterus. 

On  one  side  the  ovary  is  attached  by  a  broad  base,  the  hilum,  to 
the  broad  ligament.  Elsewhere  the  surface  of  the  ovary  is  covered 
by  a  modified  peritoneum.  At  the  hilum  the  tissues  of  the  broad 
ligament  pass  into  the  ovary  and  spread  out  there  to  form  the  ovarian 


Fig.  243.- — Ovary  opened  by  Longitudinal  Incision.  Ovum  has  Escaped  ihrough 
Tear  in  Surface.  Cavity  of  follicle  filled  with  blood  clot  (corpus  haemorrhagicum)  and 
irregular  projections  compo.sed  of  lutein  cells.     (KoUmann's  .\tlas.) 


stroma.  This  consists  of  fibrous  connective  tissue  rich  in  elastic 
fibres  and  containing  many  smooth  muscle  cells.  In  the  deeper  cen- 
tral portion  of  the  organ,  stroma  alone  is  found.  Here  it  contains 
many  large  blood-vessels,  and  constitutes  the  medulla  or  zona  vas- 
culosa  of  the  ovary  (Fig.  244,  2).  From  the  medulla  the  stroma  radi- 
ates toward  the  surface  of  the  ovary  and  becomes  interspersed  with 
glandular  elements  forming  the  ovarian  cortex  (Fig.  244,  3,  3').  At 
the  surface  of  the  ovary,  just  beneath  the  peritoneum,  the  stroma 
forms  a  rather  dense  layer  (;f  fibrous  tissue,  the  tunica  albuginea.  At 
the  margin  of  the  peritoneal  surface  of  the  ovary  the  connective  tissue 
of  the  peritoneum  becomes  continuous  with  the  stroma  of  the  ovary, 
while  the  flat  mesothelium  of  the  general  peritoneum  is  replaced 
by  a  single  layer  of  cuboidal  cells,  which  covers  the  surface  of  the 


354 


THE  ORGANS 


ovary  and  is  known  from  its  function  as  the  germinal  epithelium 
(Fig.  245,  he).  The  parenchyma  or  secreting  portion  of  the  ovary 
consists  of  peculiar  glandular  elements,  the  Graafian  follicles. 

The  structure  of  the  Graafian  follicle  can  be  best  appreciated 
by  studying  its  development.  The  follicles  originate  from  the  ger- 
minal epithelium  during  foetal  life.  At  this  time  the  germinal  epithe- 
lium is  proliferating,  and  certain  of  its  cells  differentiate  into  larger 


Fig.  244. — Semidiagrammatic  Drawing  of  Part  of  Cortex  and  Medulla  of  Cat's 
Ovary.  (From  Schron,  in  Quain's"  Anatomy.")  i,  Germinal  epithelium,  beneath  which 
is  3,  the  tunica  albuginea;  2,  medulla,  containing  large  blood-vessels,  4;  2,2',  fibrous 
stroma,  arranged  around  mature  Graafian  follicle  as  its  theca  folliculi;  3',  stroma  of  cor- 
tex; 5,  small  (primitive)  Graafian  follicles  near  surface;  6,  same  deeper  in  cortex;  7,  later 
stage  of  Graafian  folHcle,  beginning  of  cavity;  8  and  8',  still  later  stages  in  development 
of  follicle;  9,  mature  follicle;  a,  stratum  granulosum;  h,  germ  hill;  c,  ovum;  d,  nucleus 
(germinal  vesicle);  e,  nucleolus  (germinal  spot). 


spherical  cells — primitive  ova  (Fig.  245,  op).  The  primitive  ova  pass 
down  into  the  stroma  accompanied  by  a  considerable  number  of  the 
undifferentiated  cells  of  the  germinal  epithelium.  A  cord-like  mass 
of  cells  is  thus  formed,  extending  from  the  surface  into  the  stroma. 
This  is  known  a.5  Pfliiger's  egg  cord  (Fig.  245).  Each  cord  usually 
contains  several  ova.  In  some  cases  the  differentiation  of  the  ova 
cells  does  not  occur  upon  the  surface  but  in  the  cords  after  they  have 
extended  down  from  the  surface.  The  connection  of  the  cord  with 
the  surface  epithelium  is  next  broken  so  that  each  cord  becomes 
completely  surrounded  by  stroma.  It  is  now  known  as  an  egg  nest 
(Fig.  245).  During  this  process,  proliferation  of  the  epithelial  cells 
of  the  cords  and  nests  has  been  going  on,  and  each  ovum  surrounded. 


THE  REPRODUCTIVE  SYSTEM  355 

by  a  layer  of  epithelial  cells  becomes  separated  from  its  neighbors 
(Fig.  245,  fp).  This  central  o\aim  surrounded  by  a  single  layer  of 
epithehal  cells  (follicular  cells)  is  the  primitive  Graafian  follicle  (Fig. 
245,//?,  Fig.  246,  and  Fig.  247,  a).  Rarely  a  follicle  may  contain  more 
than  one  o\-um,  of  which,  however,  only  one  goes  on  to  maturity, 
the  others  degenerating.  The  follicle  increases  in  size,  mainly  on 
account  of  proHferation  of  the  follicular  cells,  which  soon  form  several 
layers  instead  of  a  single  layer,  but  also  partly  on  account  of  growth  of 


Fig.  245. — From  Transverse  Section  of  Ovarjr  of  Xevv-burn  Child.  X280  (Sobotta). 
Shows  primitive  ova  in  Kerminal  e])ithelium;  Pfliiger's  egg  cords  and  nests  of  cells;  c, 
capillaries;  he,  germinal  epithelium;  sir,  stroma;//),  primitive  follicles;  op,  primitive  ova. 

the  ovum  itself  (Fig.  247).  The  latter  now  leaves  the  centre  of  the 
follicle  and  takes  up  an  eccentric  position.  At  the  same  time  a  cavity 
(or  several  small  cavities  which  later  unite)  appears  near  the  centre 
of  the  follicle  (Fig.  247,  e  and  Y\g.  244,  7).  This  is  filled  with  fluid 
which  seems  to  be  in  part  a  secretion  of  the  follicular  cells,  in  part  a 
result  of  their  disintegration.  The  cavity  is  known  as  the  follicular 
cavity  or  antrum,  the  fluid  as  the  liquor  folliculi.  Lining  the  follicular 
cavity  are  several  rows  of  follicular  cells  with  granular  protoplasm — 
the  stratum  gramdosiim.  With  increase  in  the  liquor  folliculi  the 
ovum  becomes  still  further  i)ressed  to  one  side  of  the  follicle,  where, 
surrounded  by  an  accumulation  of  foliic  ulur  ( ells,  it  forms  a  distinct 
projection  into  the  cavity  (Fig.  249,  and  I''ig.  244,  8  and  9).     This 


356 


THE  ORGANS 


is  known  as  the  germ  hill  (discus  proligerus — cumulus  ovigerus) .  The 
cells  of  the  germ  hill  nearest  the  ovum  become  columnar  and  arranged 
in  a  regular  single  layer  around  the  ovum — the  corona  radiata  (Fig. 
250).  The  ovarian  stroma  immediately  surrounding  the  Graafian 
follicle  becomes  somewhat  modified  to  form  a  sheath  for  the  follicle — 


Fig.  246. — Vertical  Section  through  Cortex  of  Ovary  of  Young  Girl.  X 190.  (Bohm 
and  von  Davidoif.)  a,  Germinal  epithelium;  b,  tunica  albuginea;  c,  follicular  epithe- 
lium; d,  ovum;  e,  primitive  Graafian  follicles  in  ovarian  cortex;  /,  granular  layer  of 
large  Graafian  follicle. 


the  theca  folliculi  (Fig.  248).  This  consists  of  two  layers,  an  outer 
more  dense  fibrous  layer,  the  tunica  fibrosa,  and  an  inner  more  cellular 
and  vascular,  the  tunica  vasculosa.  Between  the  theca  folHculi  and 
the  stratum  granulosum  is  an  apparently  structureless  basement 
membrane. 

While  these  changes  are  taking  place  in  the  follicle,  the  ovum  is 
also  undergoing  development.     The  ovum  of  the  primitive  follicle 


THE  REPRODUCTIVE  SYSTEiNI  357 

is  a  spherical  cell,  having  a  diameter  of  from  40  to  yo/f  and  the  struc- 
ture of  a  typical  cell.  The  nucleus  or  germinal  vesicle  (so  called  on 
account  of  the  part  it  takes  in  reproduction)  is  about  half  the  diameter 
of  the  cell  and  is  spherical  and  centrally  placed  (Fig.  247).  It  is 
surrounded  by  a  double-contoured  nuclear  membrane,  and  contains  a 
distinct  chromatic  network  and  nucleolus  or  gcnninal  spot.  The 
cytoplasm  is  quite  easily  differentiated  into  a  spongioplasm  network 
and  a  homogeneous  hyaloplasm.  Such  ova  are  present  in  all  active 
ovaries,  i.e..  during  the  childbearing  period,  but  are  especially  numer- 
ous in  the  ovarv  of  the  infant  and  child  (Fig.  246). 


farqf^ 


Fig.  247. — From -Section  through  Cortex  of  .\pe's  Ovary.  X150.  (Szymonowicz.) 
a,  Primitive  follicle;  b,  ovum,  with  nucleus  and  nucleolus;  c,  zona  pellucida;  d,  follicular 
epithelium;  c,  follicular  cavity;/,  ovarian  stroma;  g,  blood-vessel  in  stroma. 

With  the  development  of  the  follicle  the  ovum  increases  in  size 
and  becomes  surrounded  by  a  clear  membrane,  the  zona  pellucida, 
believed  by  some  to  be  a  cuticular  formation  deposited  by  the  egg 
cell,  by  others  to  be  a  product  of  the  surrounding  follicular  cells. 
Minute  canals  extend  into  the  zona  pellucida  from  its  outer  surface. 
'Ihese  contain  processes  of  the  cells  of  the  corona  radiata.  A  narrow 
cleft,  the  perivitelline  space,  has  been  described  as  separating  the  ovum 
from  the  zona  pellucida.  During  the  growth  of  the  ovum  its  cyto- 
plasm becomes  coarsely  granular  from  the  development  of  yolk  or 
deutoplasm  granules  (Fig.  250).  Immediately  surrounding  the 
nucleus,  and  just  beneath  the  zona  i)elluci<la,  the  egg  protoplasm  is 
fairly  free  from  y(jlk  granules. 

'J'he  further  maturation  of  the  ovum,  which  is  necessary  before  tiie 


358  THE  ORGANS 

egg  cell  is  in  condition  to  be  fertilized,  consists  in  changes  in  the 
chromatic  elements  of  the  nucleus,  which  result  in  the  extrusion  of 
the  polar  bodies,  and  apparently  have  as  their  main  object  the  reduc- 
tion in  number  of  chromosomes  to  one-half  the  number  characteristic 
of  the  species.  This  process  has  been  described  (page  58).  In 
many  of  the  lower  animals  maturation  of  the  ovum  is  completed 
outside  the  ovary.  In  man  and  the  higher  animals  the  entire  process 
takes  place  within  the  ovary,  the  second  polar  body  being  extruded 
just  before  the  escape  of  the  ovum  from  its  follicle. 


-b 


Fig.  248. — ^Section  through  Graafian  Follicle  of  Ape's  Ovary.  X90.  (Szymono- 
wicz.)  Later  stage  of  development  than  Fig.  228.  a,  Germ  hill;  b,  ovum  with  clear 
zona  pellucida,  germinal  vesicle,  and  germinal  spot;  d,  follicular  epithelium  (membrana 
granulosa);  e,  follicular  cavity;/,  theca  folliculi;  g,  blood-vessel. 

The  youngest  of  the  Graafian  follicles  are  found  just  under  the 
tunica  albuginea  near  the  germinal  epithelium,  from  which  they  orig- 
inate (Fig.  244,  5).  As  the  follicle  matures  it  passes  deeper  into  the 
cortex.  With  complete  maturity  the  follicle  usually  assumes  macro- 
scopic proportions — 8  to  12  mm. — and  often  occupies  the  entire 
thickness  of  the  cortex,  its  theca  at  one  point  touching  the  tunica 
albuginea.  Thinning  of  the  follicular  wall  nearest  the  surface  of  the 
ovary  next  takes  place  (Fig.  251),  while  at  the  same  time  an  increase 
in  the  liquor  folliculi  determines  increased  intrafollicular  pressure. 
This  results  in  rupture  of  the  Graafian  follicle  and  the  discharge  of 
its  ovum,  together  with  the  liquor  folliculi  and  some  of  the  follicular 
cells. 


THE  REPRODUCTIVE  SYSTEM 


359 


An  escape  of  blood  into  the  follicle  from  the  torn  vessels  of  the 
theca  always  accompanies  the  discharge  of  the  ovum.  The  follicle 
again  becomes  a  closed  cavity,  while  the  contained  blood  clot  becomes 
organized  by  the  ingrowth  of  vessels  from  the  theca,  to  form  the  corpus 
Jiczniorrhagicum  (Fig.  252),  which  represents  the  earliest  stage  in  the 
development  of  the  corpus  lutcum. 


Fig.  249.^ — Graafian  Follicle  and  Contained  Ovum  of  Cat;  directly  rei)roduced 
from  a  photograph  of  a  preparation  by  Dahlgren.  X  235.  (From  "The  Cell  in  Devel- 
opment and  Inheritance,"  Prof.  E.  B.  Wilson;  The  Macmillan  Company,  publishers.) 
The  ovum  is  seen  lying  in  the  Graafian  follicle  within  the  germ  hill,  the  cells  of  the 
latter  immediately  surrounding  the  ovum  forming  the  corona  radiata.  The  clear  zone 
within  the  corona  is  the  zona  pellucida,  within  which  are  the  egg  jirotoplasm, 
nucleus,  and  nucleolus.  Encircling  the  follicle  is  the  connective  tissue  of  the  theca 
folliculi. 


The  corpus  luleum  (Fig.  253),  which  replaces  the  corpus  haimor- 
rhagicum,  consists  of  large  yellow  cells — lutein  cells — and  of  connec- 
tive tissue.  The  latter  with  its  blood-vessels  is  derived  from  the 
inner  layer  of  the  theca.  The  origin  of  the  lutein  cells  is  not  clear. 
They  are  described  by  some  as  derived  from  the  connective-tissue 
cells  of  the  theca;  by  others  as  the  result  of  i)roliferation  of  the  cells 
of  the  stratum  granulosum.  I'hc  cells  have  a  yellow  color  from  the 
presence  of  fatty  (lutein)  granules  in  their  protoplasm,  and  it  is  to 


360 


THE  ORGz\NS 


these  granules  that  the  characteristic  yellow  color  of  the  corpus 
luteum  is  due.  A  definite  cellular  structure  with  a  supporting  con- 
nective-tissue framework  thus  replaces  the  corpus  haemorrhagicum, 
remains  of  which  are  usually  present  in  the  shape  of  orange-colored 
crystals  of  haematoidin.  By  degeneration  and  subsequent  absorption 
of  its  tissues  the. corpus  luteum  becomes  gradually  reduced  in  size, 


Corona 
radiata 


Yolk 
granules. 


Zona 
pellucida 


Fig.  250. — From  a  Section  of  a  Human  Ovum.  Section  taken  from  the  ovary  of  a 
12  year  old  girl.  The  ovum  lies  in  a  large  mature  Graafian  follicle  and  is  surrounded 
by  the  cells  of  the  "germ  hill"  (the  inner  edge  of  which  is  shown  in  the  upper  left-hand 
corner  of  the  figure) .     Photograph.     (Bailey  and  Miller.) 

loses  its  yellow  color,  and  is  then  known  as  the  corpus  albicans.  This 
also  is  mostly  absorbed,  being  finally  represented  merely  by  a  small 
area  of  fibrous  tissue. 

Corpora  lutea  are  divided  into  true  corpora  lutea  (corpora  lutea 
vera  or  corpora  lutea  of  pregnancy)  and  false  corpora  lutea  (corpora 
lutea  spuria).  The  former  replace  follicles  whose  ova  have  under- 
gone fertilization,  the  latter,  follicles  whose  ova  have  not  been  fer- 


THE  REPRODUCTIVE  SYSTEM 


361 


Germinal 

epilhehum 


^^v^^p?^i^£_    Stratum 
f^'-"'' '-  >^^'/  .'j^  granulosum 


■«=>>■ . 


v^. 


Tunica  albugmea  \'<    ^^    ^^  ^ 


Germ  hill  -p^eca  folhculi 

with  ovum        (vascular  layer) 


Theca  foUicuIi  (fibrous  layer) . 


It  J 


Fig.   251. — Iruin  icLliun  uf  Human  Ovar\-,  showing  mature  Graafian  follicle  ready- 
to  rupture.     (Kollmann's  Atlas.) 


Point  of  rupture 


Lutein  cells 


Corpus  haemorrhagicum 


Blood  vessel  of  theca 


•Cavity  of  follicle 


■Theca  folliculi 


Ovarian  stroma 


Stratum  granulosum 


Fig.  252. — From  Section  of  Human  Ovary,  showing  early  stage  in  formation  of  Cor[)us 
I^uteum.     (Kollmann's  .\tlas.) 


362 


THE  ORGANS 


tilized.  The  structure  of  both  is  similar,  but  the  true  corpus  luteum 
is  larger,  and  both  it  and  its  corpus  albicans  are  slower  in  passing 
through  their  retrogressive  changes,  thus  remaining  much  longer  in 
the  ovary. 

While  the  function  of  the  corpus  luteum  is  not  known,  the  recent 
experiments  of  Fraenkel  seem  to  be  confirmatory  of  the  theory 
advanced  by  Born,  that  the  corpus  luteum  is  a  gland  having  an  inter- 

Point  of  rupture 


Connective  tissue 


Remnant  of  corpus 
hasmorrhagicum 


Blood  vessel 
of  theca 


Lutein  cells 


Connective  tissue 
from  theca 


Theca  f  ollicuH 


Blood  vessels 
of  theca 


Fig.  253. — From  Section  of  Human  Ovary,  showing  later  stage  of  Corpus  Luteum  than 
Fig.  252.     (Kollmann's  Atlas.) 


nal  secretion,  which  appears  to  have  some  influence  upon  the  attach- 
ment of  the  fecundated  ovum  to  the  uterus  and  upon  its  nutrition 
during  the  first  few  weeks  of  its  development.  According  to  Fraenkel 
the  corpus  luteum  is  a  periodically  rejuvenated  ovarian  gland,  which 
gives  to  the  uterus  a  cyclic  nutritional  impulse,  which  prepares  it  for 
the  implantation  of  the  ovum  or  favors  menstruation  whenever  the 
ovum  is  not  fertilized. 


THE  REPRODUCTIVE  SYSTEM  363 

Of  the  large  number  of  ova — estimated  at  seventy-two  thousand  in 
the  human  ovaries — only  comparatively  few,  according  to  Henle 
about  four  hundred,  reach  maturity.  The  majority  undergo,  to- 
gether with  their  follicles,  retrogressive  changes  known  as  atresia 
of  the  foUicle.  The  nucleus  of  the  ovum,  as  well  as  the  nuclei  of 
the  folHcular  cells,  passes  through  a  series  of  chromatolytic  changes, 
or  in  some  cases  apparently  simply  atrophies.  The  cell  bodies  un- 
dergo fatty  or  albuminous  degeneration  and  the  cells  become  reduced 
to  a  homogeneous  mass,  which  is  finally  absorbed,  leaving  in  its 
place  a  connective-tissue  scar,  probably  the  remains  of  the  theca 
folliculi. 

Blood-vessels. — The  arteries,  branches  of  the  ovarian  and  uterine, 
enter  the  ovary  at  the  hilum  and  ramify  in  the  medulla.  From  these 
are  given  oft"  branches  which  pass  to  the  cortex  and  end  in  a  capillary 
network  in  the  tunica  albuginea.  In  the  outer  layer  of  the  theca 
folHculi  the  capillaries  form  a  wide-meshed  network,  which  gives 
rise  to  a  fine-meshed  network  of  capillaries  in  the  inner  layer  of  the 
theca.  From  the  capillaries  veins  arise  which  form  a  plexus  in  the 
medulla  and  leave  the  ovary  at  the  hilum. 

Lymphatics. — These  begin  as  small  lymph  spaces  in  the  cortex, 
which  communicate  with  more  definite  lymph  vessels  in  the  medulla, 
the  latter  leaving  the  organ  at  the  hilum. 

Nerves.— Medullated  and  non-medullated  fibres  enter  the  ovary 
at  the  hilum  and  follow  the  course  taken  by  the  blood-vessels.  Many 
of  the  fibres  end  in  the  vessel  walls;  others  form  plexuses  around  the 
follicle  and  end  in  the  theca  folHcuh.  Some  describe  fibres  as 
passing  through  the  theca  and  ending  in  the  follicular  epithelium. 
Others  claim  that  nerve  fibres  do  not  enter  the  follicle  proper. 
Groups  of  sympathetic  ganglion  cells  occur  in  the  medulla  near  the 
hilum. 

As  is  the  case  with  the  testicle,  certain  rudimentary  organs,  the 
remains  of  ffjctal  structures,  are  found  connected  with  the  ovary. 

The  paroophoron  consists  of  a  number  of  cords  or  tubules  of  epi- 
thelial cells,  sometimes  ciliated,  sometimes  non-ciliated.  It  is  found 
in  the  medulla,  or,  more  commonly,  in  the  connective  tissue  of  the 
hilum. 

The  epoophoron  is  a  similar  structure  found  in  the  folds  of  the 
broad  ligament.  Its  tubules  open  into  a  duct  known  as  Gartner's 
duct.  In  man  this  duct  ends  blindly.  In  some  of  the  lower  animals 
it  opens  into  the  vagina.     Both  paroophoron  and  c])ooj)horon  are 


364 


THE  ORGANS 


remains  of  the  embryonal  mesonephros,  the  former  of  its  posterior 
segment,  the  latter  of  its  middle  segment. 

The  Oviduct 

The  oviduct  or  Fallopian  tube  is  the  excretory  duct  of  the  ovary, 
serving  for  the  transmission  of  the  discharged  ovum  from  ovary  to 
uterus.  Although  there  is  no  sharp  demarcation  between  them, 
it  is  convenient  to  divide  the  tube  into  three  segments:  (i)  The 
isthmus,  beginning  at  the  uterus  and  extending  about  one-third  the 


Fig.  254. — Cross  Section  of  Oviduct  near  Uterine  End.  a,  Mucous  membrane;  b, 
circular  muscle  coat;  c,  longitudinal  muscle  coat;  d,  connective  tissue  of  serous  coat. 
(Orthmann.) 

length  of  the  tube;  (2)  the  ampulla,  about  twice  the  diameter  of  the 
isthmus,  and  occupying  somewhat  more  than  the  middle  third; 
and  (3)  the  fimbriated  or  ovarian  extremity. 

The  walls  of  the  oviduct  consist  of  three  coats:  (i)  Mucous,  (2) 
muscular,  and  (3)  serous  (Figs.  254  and  255). 

The  mucous  membrane  presents  numerous  longitudinal  foldings. 
In  the  embryo  four  of  these  folds  can  usually  be  distinguished,  and 
these  are  known  as  primary  folds.  In  the  adult  many  secondary 
folds  have  developed  upon  the  primary,  especially  in  the  ampulla 
and  fimbriated  extremity  where  the  folds  are  high  and  complicated 
(Fig.  255).  The  epithelium  lining  the  tube  is  of  the  simple  columnar 
ciliated  type,  and  completely  covers  the  foldings  of  the  mucous  mem- 


THE  REPRODUCTIVE  SYSTEM  365 

brane.  The  ciliary  motion  is  toward  the  uterus.  The  stroma  con- 
sists of  a  cellular  connective  tissue,  quite  compact  in  structure  in  the 
isthmus,  where  the  folds  are  low,  more  loosely  arranged  in  the  high 
folds  of  the  ampulla  and  fimbriated  extremity. 

The  muscular  coat  consists  of  an  inner  circular  and  an  outer  longi- 
tudinal layer.  The  latter  is  a  comparatively  thin  layer  in  the  isth- 
mus, consists  of  discontinuous  groups  of  muscle  cells  in  the  ampulla, 
and  in  the  fimbriated  extremity  is  frequently  absent. 


'V-         '-  ^r!;\-'''n?^ ' 


-I* 


% 


Fig.   255. — Cross  Section  of  Oviduct  near  Fimbriated  Extremity,  showing  complicated 
foldings  of  mucous  membrane.     (Orthmann.) 

The  serous  coat  has  the  usual  structure  of  peritoneum. 

The  larger  blood-vessels  run  in  the  stroma  along  the  bases  of  the 
folds.  They  send  off  branches  which  give  rise  to  a  dense  capillary 
network  in  the  stroma. 

Of  the  lymphatics  of  the  tube  little  is  known. 

The  nerves  form  a  rich  plexus  in  the  stroma,  from  which  branches 
pass  to  the  blood-vessels  and  muscular  tissue  of  the  walls  of  the  tube 
and  internally  as  far  as  the  epithelial  lining. 

TECHNIC 

(i)  Child's  Ovary.— Remove  the  ovary  of  a  new-born  child,  being  careful  not 
to  touch  the  surface  epithcHum,  fix  in  Zenker's  fluid  (technic  9,  p.  8),  and  harden 
in  alcohol.  Cut  sections  of  the  entire  organ  through  the  hilum.  Stain  with 
ha;niatoxylin-eosin  (technic  i,  p.  20)  and  mount  in  balsam. 

(2)  For  the  purpose  of  studying  the  Graafian  follicle  in  the  different  stages  of 


366 


THE  ORGANS 


its  development  remove  an  ovary  from  an  adult  cat  or  dog  and  treat  as  above. 

Technic  (i).     These  sections  also,  as  a  rule,  are  satisfactory  for  the  study  of  the 

corpus  luteum. 

(3)  The  adult  human  ovary  is  little  used  for  histological  purposes  on  account 

of  the  few  foUicles  it  usually  contains  and  its  proneness  to  pathological  changes. 
Its  study  is,  however,  so  extremely  important,  especially 
\  with  reference  to  the  pathology  of  the  ovary,  that  if  possi- 

ble a  normal  human  ovary  should  be  obtained  from  a 
young  subject  for  purposes  of  comparison  with  the  above. 
Technic  (i). 

(4)  For  studying  the  egg  cords  of  Pfiiiger  and  their 
relation  to  the  germ  epithelium,  ovaries  of  the  human 
foetus,  and  of  very  young  cats,  dogs,  and  rabbits  are  satis- 
factory.    Technic  (i). 

(5)  Sections  of  the  frmbriated  end  of  the  oviduct 
are  usually  found  in  the  sections  of  ovary.  For  the  study  of 
other  parts  of  the  tube,  cut  out  thin  pieces  from  different 
regions,  fix  in  formalin-MuUer's  fluid,  stain  transverse  sec- 
tions with  h^ematoxylin-eosin,  and  mount  in  balsam. 

The  Uterus 

The  wall  of  the  uterus  consists  of  three  coats 
which  from  without  inward  are  serous,  muscular, 
and  mucous. 

The  serous  coat  is  a  reflection  of  the  peritoneum, 
and  has  the  usual  structure  of  a  serous  membrane. 
The  muscularis  consists  of  bundles  of  smooth 
muscle  cells  separated  by  connective  tissue.  The 
muscle  has  a  general  arrangement  into  three 
layers,  an  inner,  a  middle,  and  an  outer,  which  are 
distinct  in  the  cervix,  but  not  well  defined  in  the 
body  and  fundus. 

The  inner  layer — stratum  submucosum — is 
mainly  longitudinal,  although  some  obliquely 
running  bundles  are  usually  present. 

The  middle  layer — called  from  the  large  venous 

channels  which  it  contains,  the  stratum  vasculare 

■ — is  the  thickest  of  the  three  layers,  forming  the 

main  bulk  of  the  muscular  wall.     It  consists  mainly  of  circularly 

disposed  muscle  bundles. 

The  outer  layer — stratum  supravasculare — is  thin  and  consists 
partly  of  circular  bundles,  partly  of  longitudinal.  The  latter  pre- 
dominate and  form  a  fairly  distinct  layer  just  beneath  the  serosa. 


Fig.  256. — Muscle 
cells  from  (a)  non- 
pregnant uterus;  b, 
pregnant  uterus; 
drawn  to  same  scale. 
(Sellheim.) 


THE  REPRODUCTIVE  SYSTEM 


367 


The  muscle  cells  of  the  uterus  are  long  spindle-shaped  elements, 
some  having  pointed,  others  blunt,  branched,  or  frayed  ends.  In  the 
virgin  uterus  they  have  a  length  of  from  40  to  6o,«.  During  preg- 
nancy the  muscular  tissue  of  the  uterus  is  greatly  increased.  This 
is  due  partly  to  increase  in  the  number,  partly  to  increase  in  the 
size  of  the  muscle  cells.  At  term  the  muscle  cells  frequently  have 
a  length  of  from  250  to  6oo/<.     (Fig.  256.) 

The  mucous  membrane.  As  the  mucosa  presents  marked  variation 
in  structure,  dependent  upon  the  functional  condition  of  the  organ, 
it  is  necessary  to  describe: 

1.  The  mucosa  of  the  resting 
uterus. 

2.  The  mucosa  of  the  men- 
struating uterus. 

3.  The  mucosa  of  the  prci^ 
nant  uterus. 

I.  The  Mucosa  of  the  Res  i 
iNG  Uterus 

This  is  from  i  to  2  mm.  thick 
and  consists  of  a  stroma,  glands. 
and  a  lining  epithelium  (Fig. 
257).  The  stroma  resembles 
embryonal  connective  tissu( 
consisting  of  fine  fibrils  and 
long,  irregular  branching  cells 
which  form  a  sort  of  network, 
the  me.shes  of  which  are  filled  in 
with  lymphoid  cells  and  leuco- 
cytes. The  epithehum  is  of  the 
simple  high  columnar  ciliated 

variety,  the  ciliary  motion  being  toward  the  cervix.  A  basement 
membrane  separates  the  epithelium  from  the  underlying  stroma.  The 
glands  are  simple  forked  tubules  lined  by  a  single  layer  of  columnar 
ciliated  cells  resting  upon  a  basement  membrane  and  continuous 
with  the  surface  cells.  The  glands  extend  completely  through  the 
stroma.  Near  the  surface  they  run  a  comparatively  straight  course. 
Deeper  in  the  stroma  their  course  is  more  tortuous,  while  the  fundus 
is  frequently  turned  at  right  angles  to  the  rest  of  the  tubule. 

In  the  cervix  the  stroma  is  firmer  and  less  cellular,  and  the  mu- 


FiG.  257. — From  Uterus  of  Young  Woman. 
(Bohm  and  vonDavidoff;  preparation  by  Dr. 
J.  Amann.)  X34.  a,  Mucous  membrane; 
b,  surface  epithelium;  c,  gland;  e,  muscle. 


368  THE  ORGANS 

cous  membrane  is  thicker  and  presents  numerous  folds — the  pliccB 

palmatce.     The  epithehum  is  higher  than  in  the  body  of  the  organ. 

In  addition  to  glands  like  those  found  in  the  body  of  the  uterus,  the 

cervical  mucosa  contains  peculiar  short,  sac-like  invaginations,  lined 

with  a  continuation  of  the  surface  epithelium,  which  secrete  a  glairy 

J-  mucus.     Closure  of  the  mouths 

,,-• "  -..^  of  some  of  these  sacs  frequently 

-''..--■,-:'- ^^''^0^  occurs,  leading  to  the  formation 

jk  of  retention  cysts,  the  so-called 

,  'm  ovula  Nabothi.     At  about  the 

^  -  -.|l^ — -  -  -  _-    Vr"' "        '     junction  of  middle  and  lower 

h |v  -  -      ' '. i-^ '^     thirds  of  the  cervical  canal  a 

II,      \  /        '  change  takes  place  in  the  epi- 

^ '"""X ,        ,  ,  --   ^  thelium.       Here    the     simple 

..-"^|;  -if  columnar    ciliated    epithehum 

/  '     ..^.:^-.-,..-:^r.^,        '""      h     of  the  upper  part  of  the  cervix 

Fig.  258.-From  Section  of  Dog's  Cervix,    gradually    passes  over  into  a 

X4-    (Technic  2,  p.  379.)    a,  Cervical  canal;    stratified     Squamous     epithe- 

h,  mucosa;    c,   folds   of   mucosa    (plicae   pal- 

mata;);  d,  muscle  layers  of  cervix;  e,  epithe-  hum.  Near    the    external    OS 

Hum  of  vagina  and  vaginal  surface  of  cervix;  papiH^  appear,     the     vaginal 

/,  vagmal  epithelium;  g,  vaginal  mucosa;  h,  ^    ^  ^^        '             _         °  ^ 

submucosa  and  muscularis  of  vagina;  i,  blood-  surface  of     the     cervix     being 

covered  with  a  stratified 
squamous  epithelium  with  underlying  papillae  similar  to  and  con- 
tinuous with  that  of  the  vagina. 

Near  the  external  os  the  epithelium  changes  over  into  the  strati- 
fied squamous  epithelium  with  underlying  papillae,  similar  to  that 
of  the  external  surface  of  the  cervix. 


2.  The  Mucosa  of  the  Menstruating  Uterus 

This  consists  of  the  same  structural  elements  as  the  mucosa  of 
the  resting  uterus:  stroma,  glands,  and  lining  epithelium.  These, 
however,  undergo  certain  changes  which  may  be  conveniently 
divided  into  three  stages : 

{a)  The  stage  of  preparation. 

(&)  The  stage  of  menstruation  proper. 

(c)  The  stage  of  reparation. 

{a)  The  Stage  of  Preparation. — This  begins  several  days 
before  the  actual  flow  of  blood,  and  is  marked  by  an  intense 
hypersemia  determining  a  swelling  and  growth  of  the  entire  mucosa. 


THE  REPRODUCTIVE  SYSTEM 


369 


The  blood-vessels,  especially  the  capillaries  and  veins,  become  greatly 
distended,  thus  contributing  largely  to  the  increase  in  thickness  of 
the  mucosa.  There  are  also  proliferation  of  the  connective-tissue 
cells,  an  increase  in  the  number  of  leucocytes,  and  a  growth  of  the 
uterine  glands.  The  surface  at  the  same  time  becomes  irregular,  the 
glands  opening  into  deep  pits  or 
depressions,  and  the  glands  them- 
selves become  more  tortuous  and 
their  lumina  more  widely  open. 
The  mucous  membrane  has  now 
reached  a  thickness  of  about  6 
mm.,  and  is  known  as  the  de- 
cidua  menstrualis  (Fig.  259). 

{h)  The  Stage  of  Men- 
struation Proper. — This  is 
marked  by  the  escape  of  blood 
from  the  engorged  vessels  and 
the  appearance  of  the  external 
phenomena  of  menstruation.. 
The  blood  escapes  partly  by  rup- 
ture of  the  vessel  walls,  partly  by 
diapedesis.  The  hemorrhage  is 
at  first  subepithelial,  but  the 
epithelium  soon  gives  way  and 
the  blood  escapes  into  the  cavity 
of  the  uterus.  Much  difference 
of  opinion  exists  as  to  the  amount 
of  epithelial  destruction  during 
menstruation,  some  claiming 
that  the  entire  epithelium  is  de- 
stroyed with  each  menstrual  period,  others  that  the  epithelium  re- 
mains almost  intact.  Complete  destruction  of  the  e])ithelium  is 
hardly  compatible  with  the  restoration  of  the  ejnthelium  which  always 
follows  menstruation.  While  there  is  undoubtedly  destruction  of 
most  or  all  of  the  surface  epithelium  and  of  the  glands  to  some  con- 
siderable dei)th,  the  deeper  portions  of  the  glands  always  remain  to 
take  |)art  in  the  succeeding  regenerative  phenomena. 

{c)  Tin-;  Stac;!-:  of  Rki'Akaiion. — After  from  three  to  live  days 
the  blecfjing  from  the  uterine  mucosa  ceases  and  the  return  to  the 
resting  condition  begins.     This  is  marked  by  disaj)pearan(e  ot  the 


Fig.  259. — Section 
Membrane  of  Virgin  Uterus  during  First 
Day  of  Menstruation.  X30.  (Sciiaper.) 
<;,  Surface  epithelium;  b,  disintegrating 
surface;  r,  pit-like  depression  in  mucous 
membrane;  d,  excretory  duct;  e,  blood- 
vessels; g,  gland  tubule;  //,  dilated  gland 
tulnile;   m,  muscularis. 


370  THE  ORGANS 

congestion,  by  decrease  in  thickness  of  the  mucosa  and  in  the  size  of 
the  glands,  and  by  restoration  of  the  surface  epithelium. 

3.  The  Mucosa  of  the  Pregnant  Uterus. 

This  is  known  as  the  decidua  graviditatis,  and  presents  changes  in 
structure  somewhat  similar  to  those  which  occur  during  menstrua- 
tion, but  more  extensive.     It  is  divided  into  three  parts: 

(a)  The  decidua  serotina  or  decidua  basalis — that  part  of  the 
mucosa  to  which  the  ovum  is  attached. 

(b)  The  decidua  refiexa  or  decidua  capsularis — that  part  of  the 
mucosa  which  surrounds  the  ovum. 

(c)  The  decidua  vera — which  consist  of  all  the  remaining  mucosa. 
The  development  of  the  decidua  vera  resembles  the  changes  which 

take  place  in  the  mucosa  during  menstruation.  There  is  the  same 
thickening  of  the  mucosa,  and  this  thickening  is  due  to  the  same 
factor,  i.e.,  distention  of  the  blood-vessels  and  proliferation  of  the 
tissue  elements.  These  changes  are,  however,  much  more  extensive 
than  during  menstruation.  The  superficial  part  of  the  stroma 
between  the  mouths  of  the  glands  becomes  quite  dense  and  firm, 
forming  the  compact  layer.  The  deeper  part  of  the  stroma  contains 
numerous  cavities,  which  are  the  lumina  of  the  now  widely  distended 
and  tortuous  glands.     This  is  known  as  the  spongy  layer. 

Within  the  stroma,  especially  of  the  compact  layer,  develop  the 
so-called  decidual  cells.  These  are  peculiar  typical  cells  derived  from 
connective  tissue.  They  are  of  large  size  (30  to  100/^),  vary  greatly 
in  shape,  and  in  the  later  months  of  pregnancy  have  a  rather  charac- 
teristic brown  color,  which  they  impart  to  the  superficial  layers  of 
the  decidua  vera.  They  are  mostly  mononuclear,  although  poly- 
nuclear  forms  occur. 

During  the  latter  half  of  pregnancy  there  is  a  gradual  thinning  of 
the  decidua  vera,  due  apparently  to  pressure.  The  necks  of  the 
glands  in  the  compact  layer  disappear,  and  the  gland  lumina  in  the 
spongy  layer  are  changed  into  elongated  spaces,  which  lie  parallel  to 
the  muscular  layer. 

The  decidua  refiexa  and  decidua  serotina  have  at  first  the  same 
structure  as  the  decidua  vera.  The  decidua  refiexa  undergoes  hyaline 
degeneration  during  the  early  part  of  pregnancy,  and  by  the  end  of 
gestation  has  either  completely  disappeared  (Minot)  or  has  fused  with 
the  decidua  vera  (Leopold). 


THE  REPRODUCTIVE  SYSTEM  371 

The  decidua  serotina  undergoes  changes  connected  with  the 
development  of  the  placenta. 

The  Placenta^ 

The  placenta  consists  of  two  parts,  one  of  which  is  of  maternal 
origin- — placenta  uterina — the  other  of  foetal  origin — the  placenta 
fostalis.  As  it  is  in  the  placenta  that  the  interchange  takes  place 
between  the  maternal  and  the  foetal  blood,  the  relations  between  the 
maternal  and  foetal  parts  of  the  placenta  are  extremely  intimate. 
This  relation  consists  essentially  in  the  growing  out  from  the  foetal 
placenta  of  tinger-like  projections — villi — which  penetrate  the  mater- 
nal placenta,  the  latter  being  especially  modified  for  their  reception. 

The  Placenta  Fcetalis. — This  is  a  differentiated  portion  of  the 
chorion.  On  the  surface  directed  toward  the  fcetus  the  chorion  after 
the  third  month  is  covered  by  a  delicate  foetal  membrane,  the  placen- 
tal portion  of  the  amnion.  This  consists  of  a  surface  epithelium, 
resting  upon  a  layer  of  embryonal  connective  tissue  which  attaches  it 
to  the  chorion.  The  chorion  consists  of  (a)  a  compact  layer — the 
membrana  cJiorii — composed  at  first  of  embryonal,  later  of  fibrous, 
connective  tissue,  and  containing  the  main  branches  of  the  umbilical 
vessels  and  {b)  an  inner  villous  layer,  which  gives  rise  to  finger-like 
projections  which  extend  down  from  the  foetal  into  the  maternal 
placenta  and  serve  to  connect  the  two. 

The  chorionic  villi  first  appear  as  short  projections  composed 
entirely  of  epithelium.  Each  of  these  primary  villi  branches  dichoto- 
mously,  giving  rise  to  a  number  of  secondary  villi.  As  they  develop, 
the  central  portion  of  the  original  solid  epithelial  structure  is  replaced 
by  connective  tissue.  Septa  of  connective  tissue  from  the  maternal 
placenta  pass  down  among  the  villi  and  separate  them  into  groups  or 
cotyledons.  The  main  or  primary  villi  run  a  quite  straight  course  from 
the  chorion  into  the  maternal  placental  tissue,  apparently  serving  to 
secure  firm  union  between  the  two.  They  are  thus  known  as  roots  of 
attachment  or  fastening  villi  (Fig.  260) .  The  secondary  villi  are  given 
off  laterally  from  the  primary  villi,  end  freely  in  the  spaces  between 
the  latter  intervillous  si)accs  (Fig.  260) — and  are  known  -d?,  free, 
terminal  or  floating  villi  (Fig.  260). 

The  chorionic  villus  thus  ccmsists  of  a  central  core  of  connective 

'  I-'or  many  facts  as  to  ihc  structure  of  the  placenta,  the  writer  is  indebted  lo  the 
excellent  chapter  f)n  the  subject  aflrlcd  \)y  I'rof.  Alfred  Schai)er  to  the  liftli  edition  of 
Stohr's  "Textbook  of  Mistoloj^y." 


372 


THE  ORGANS 


THE  REPRODUCTIVE  SYSTEM 


373 


tissue  covered  by  a  layer  of  epithelium.  The  connective  tissue  is  of 
the  mucous  type  and  serves  for  the  transmission  of  numerous  blood- 
vessels. In  the  villi  of  early  pregnancy  the  epithelium  consists  of  an 
inner  layer  of  distinctly  outHned  cells  and  an  outer  layer  of  fused  cell 
bodies-a  syncytium  (Fig.  262,  A,  a)-containing  small  scattered 
nuclei.  The  villi  of  the  later  months  of  pregnancy  have  no  defimte 
epithelial  covering,  but  are  surrounded  by  a  dehcate  homogeneous 
membrane,  probably  the  remains  of  the  syncytium.  At  various 
points  on  the  surface  of  the  villus  are  groups  of  nuclei.     These  stam 


"Giant"  cell 


Syncytium 


Trophorierm 
mass 


Stroma  of 
villus 


mass  vulus  ->^ 

Fig.  261.— Section  of  Chorion  of  Human  Embryo  of  one  monlh  (9  mm.).     (Grosser.) 


intensely,  are  surrounded  by  a  homogeneous  protoplasm,  and  form 
knob-Uke  projections  above  the  general  surface  of  the  villus.  They 
are  known  as  cell  patches,  or  more  properly  as  nuclear  groups  (Fig. 
262  c),  and  represent  remains  of  the  nuclei  of  the  epithelium  of  the 
younger  villus.  Between  the  nuclear  groups  the  villus  is  covered 
only  by  a  thin  homogeneous  membrane.  Small  villi  usually  resemble 
more  closely  in  structure  the  younger  villus,  being  frequently  covered 
by  a  nucleated  syncytium.  Portions  of  the  syncytium,  especially 
of  older  villi,  sometimes  bec(;me  changed  into  a  peculiar  hyaline  sub- 
stance containing  numerous  channels.     This  is  known  as  canalized 


374: 


THE  ORGANS 


d—f-. 


fibrin,  and  may  form  dense  layers  upon  the  surface  of  the  chorion. 
(Fig.  261.) 

The  Placenta  Uteeina. — This  develops  from  the  decidua  sero- 
tina.  The  latter  becomes  much  thinner  than  the  rest  of  the  decidua 
(decidua  vera) ,  but  still  shows  a  division  into  a  deeper  spongy  portion 
containing  gland  tubules,  and  a  superficial  compact  portion  in  which 
are  large  numbers  of  decidual  cells.     From  the  superficial  portion 

connective-tissue  septa — placental 
septa — grow  into  the  foetal  pla- 
centa, as  described  above,  separat- 
ing its  villi  into  cotyledons.  Near 
the  margins  of  the  placenta  these 
septa  pass  to  the  chorionic  mem- 
brane and  form  beneath  it  a  thin 
membrane,  the  suhchorionic  pla- 
cental decidua.  At  the  edge  of  the 
placenta,  where  decidua  serotina 
passes  over  into  the  thicker  decidua 
vera,  there  is  a  close  attachment  of 
the  chorion  to  the  former. 

As  the  placenta  serves  as  the 
place  of  interchange  of  materials 
between  the  maternal  and  the  foetal 
circulations,  the  arrangement  of  the 
placental  blood-vessels  is  of  espe- 
cial importance.  Arterial  branches 
from  vessels  of  the  uterine  muscularis  enter  the  serotina.  In  the 
very  tortuous  course  which  these  vessels  take  through  the  serotina 
(Fig.  260)  their  walls  lose  their  muscular  and  connective- tissue  ele- 
ments and  become  reduced  to  epithehal  tubes.  These  branch  in  the 
placental  septa  and  finally  open  into  the  intervillous  spaces  along  the 
edges  of  the  cotyledons.  The  veins  take  origin  from  these  spaces 
near  the  centres  of  the  cotyledons.  The  maternal  blood  thus  passes 
through  the  intervillous  spaces  from  periphery  to  centre,  and  in  its 
course  comes  into  direct  contact  with  the  freely  terminating  chorionic 
vilH.  It  is  to  be  noted  that  the  blood-vessel  systems  of  the  mother 
and  of  the  foetus  are  both  closed  systems,  and  that  consequently 
there  is  no  direct  admixture  of  maternal  and  foetal  blood.  Inter- 
change of  materials  must  therefore  always  take  place  through  the 
capillary  walls  and  through  the  walls  of  the  chorionic  vilH.     (Fig.  260.) 


Fig.  262. — Cross  Sections  of  Human 
Chorionic  Villi  at  End  of  Pregnancy. 
X250.  (Schaper.)  A,  Small  villus;  B, 
larger  villus,  a,  Protoplasmic  coat 
(syncytium);  h,  epithelial  nucleus;  c, 
nuclear  groups;  d,  small  artery;  e,  small 
vein;  /,  capillaries. 


THE  REPRODUCTIVE  SYSTEM  375 

Blood-vessels. — The  arteries  enter  the  uterus  from  the  broad 
ligament  and  pass  to  the  stratum  vasculare  of  the  muscularis,  where 
they  undergo  extensive  ramification.  From  the  arteries  of  the  stra- 
tum vasculare  branches  pass  to  the  mucosa  and  give  rise  to  capillary 
networks,  which  surround  the  glands  and  are  especially  dense  just 
beneath  the  surface  epithelium.  From  these  capillaries  the  blood 
passes  into  a  plexus  of  veins  in  the  deeper  portion  of  the  mucosa, 
and  these  in  turn  empty  into  the  venous  plexuses  of  the  stratum  vas- 
culare. Thence  the  veins  accompany  the  arteries,  leaving  the  uterus 
through  the  broad  Ugament. 

Lymphatics. — These  begin  as  minute  spaces  in  the  stroma  and 
empty  into  the  more  definite  lymph  channels  of  the  muscularis, 
which  are  especially  well  developed  in  the  stratum  vasculare.  These 
in  turn  communicate  with  the  larger  lymph  vessels  in  the  subserous 
connective  tissue. 

Nerves. — Both  medullated  and  non-medullated  nerve  fibres  occur 
in  the  uterus.  The  latter  are  associated  with  minute  sympathetic 
ganglia  and  supply  the  muscular  tissue.  The  medullated  fibres  form 
plexuses  in  the  mucosa,  from  which  are  given  off  fine  fibres  which 
terminate  freely  between  the  cells  of  the  surface  epithelium  and  of  the 
uterine  glands. 

The  Vagina 

The  wall  of  the  vagina  consists  of  four  coats,  which  from  without 
inward  are  fibrous,  muscular,  submucous,  and  mucous. 

The  fibrous  coat  consists  of  dense  connective  tissue  with  many 
coarse  elastic  fibres.  It  serves  to  connect  the  vagina  with  the  sur- 
rounding structures. 

The  muscular  coat  is  indistinctly  divided  into  an  outer  longitudinal 
and  an  inner  circular  layer.  The  latter  is  usually  not  well  developed 
and  may  be  absent. 

The  submucosa  is  a  layer  of  loose  connective  tissue,  especially  rich 
in  elastic  fibres  and  blood-vessels.  Numerous  large  venous  channels 
give  to  the  submucosa  the  character  of  erectile  tissue. 

The  mucous  membrane  consists  of  a  papillatcd  connective-tissue 
stroma  of  mixed  fibrous  and  elastic  tissue.  The  stroma  usually  con- 
tains diffuse  lymphoid  tissue  and  more  rarely  solitary  nodules.  Cover- 
ing the  stroma  is  a  stratified  squamous  epithelium,  the  surface  cells  of 
which  are  extremely  thin.     The  surface  of  the  mucosa  is  not  smooth, 


376  THE  ORGANS 

but  is  folded  transversely,  forming  the  so-called  rugcB.  Most  au- 
thorities agree  that  glands  are  wanting  in  the  vagina,  the  mucus 
found  there  being  derived  from  the  glands  of  the  cervix. 

Blood-vessels. — The  larger  blood-vessels  run  in  the  submucosa, 
giving  off  branches  which  break  up  into  capillary  networks  in  the  sub- 
mucosa, muscularis,  and  stroma.  The  vascular  networks  have  a 
general  direction  parallel  to  the  surface.  The  capillaries  empty  into 
veins  which  form  a  plexus  of  broad  venous  channels  in  the  muscularis. 

The  L5mipliatics. — These  follow  in  general  the  distribution  of  the 
blood-vessels. 

Nerves. — Nerve  fibres  from  both  cerebro-spinal  and  sympathetic 
systems  are  found  in  the  vagina.  Medullated  (sensory)  fibres,  the 
dendrites  of  spinal  ganglion  cells,  form  plexuses  in  the  mucosa,  from 
which  are  given  off  delicate  non-medullated  terminals  to  the  epithe- 
lial cells.  Non-medullated  sympathetic  fibres  supply  the  muscularis 
and  the  muscle  of  the  vessel  walls.  Along  these  nerves  are  small 
sympathetic  ganglia. 

In  the  vestibule  the  epithelium  gradually  takes  on  the  structure  of 
epidermis.  Here  are  located  small  mucous  glands — glandulce  vestih- 
ulares  minores — especially  numerous  around  the  clitoris  and  opening 
of  the  urethra.  Larger  mucous  glands — glandulce  vestihulares  ma- 
jores,  or  glands  of  Bartholin — analogous  to  Cowper's  glands  in  the 
male,  are  also  found  in  the  walls  of  the  vestibule. 

The  clitoris  consists  mainly  of  erectile  tissue  similar  to  that  of  the 
corpora  cavernosa  of  the  penis.  It  is  covered  with  a  thin  epithelium 
with  underlying  papillae,  and  is  richly  supplied  with  nerves  having 
highly  specialized  terminations. 

Development  of  the  Urinary  and  Reproductive  Systems 

The  development  of  the  genito -urinary  system  is  complicated  by  the  appear- 
ance, and  disappearance  for  the  most  part,  of  two  sets  of  urinary  organs,  and 
the  final  formation  of  the  permanent  set.  The  three  sets,  in  the  order  of  their 
appearance,  are  the  pronephroi,  mesonephroi,  and  metanephroi.  The  first 
two  sets,  which  are  present  only  in  the  embryo  in  the  higher  animals,  are  the 
representatives  of  organs  that  function  in  the  adult  in  the  lower  vertebrates. 
They  are  also  intimately  concerned  in  the  development  of  the  efferent  duct 
system  of  the  male  reproductive  organs  in  higher  animals.  The  metanephroi,. 
generally  known  as  the  kidneys,  are  the  functional  urinary  organs  in  the  majority 
of  reptiles  and  in  all  birds  and  mammals. 

The  pronephroi  are  represented  in  the  human  embryo  of  3  to  5  mm.  by  one  or 
two  small,  condensed  masses  of  mesoderm  just  lateral  to  the  primitive  segments 


THE  REPRODUCTIVE  SYSTEM  377 

on  each  side  in  the  cervical  region.  These  masses,  which  are  probably  derived 
from  the  mesothelial  lining  of  the  body  cavity,  may  or  may  not  become  hollow, 
but  do  not  connect  with  the  pronephric  duct,  and  soon  disappear.  The  pro- 
nephric  duct  appears  about  the  same  time  as  a  derivative  of  the  mesoderm  just 
lateral  to  the  primitive  segments.  It  extends  from  the  cervical  region  to  the 
caudal  region  of  the  embryo  where  it  bends  mesially  and  opens  into  the  gut. 
These  ducts  persist  and  become  the  ducts  of  the  mesonephroi. 

The  mesonephroi  begin  to  develop  almost  as  soon  as  the  pronephroi  and  just 
caudal  to  them.  Condensations  appear  in  the  mesodermal  tissue  lateral  to  the 
primitive  segments  and  become  more  or  less  tortuous.  Lamina  appear  in  these 
condensations,  thus  forming  tubules  which  then  connect  at  one  end  with  the 
pronephric  duct  (now  the  mesonephric  or  Wolffian  duct).  The  tubules  develop 
progressively  from  before  backward  and  finally  form  a  series  extending  from  the 
cervical  region  to  the  pelvic  region  of  the  embryo.  At  the  distal  end  of  each 
tubule  a  glomerulus,  containing  branches  from  the  aorta,  develops.  The 
tubules  increase  in  length  and  number  and  come  to  form  a  pair  of  large  struc- 
tures which  project  into  the  dorsal  part  of  the  body  cavity.  These  are  often 
spoken  of  as  the  Wolffian  bodies.  They  reach  the  height  of  their  develop- 
ment during  the  fifth  or  sixth  week. 

During  the  period  of  their  existence  in  the  embryo  in  higher  animals,  the 
mesonephroi  functionate  as  urinary  organs,  not  only  through  the  agency  of  the 
glomeruli  but  also  by  means  of  the  epithelium  of  the  tubules  themselves,  among 
which  numerous  branches  of  the  posterior  cardinal  veins  ramify. 

From  the  sixth  week  on,  and  coincident  with  the  development  of  the  meta- 
nephroi  or  kidneys,  the  mesonephroi  atrophy,  leaving  finally  only  certain  parts 
which  differ  in  the  two  sexes.  In  the  male  some  of  the  tubules  in  the  cephahc 
portion  persist  as  the  vasa  efferentia,  while  a  few  in  the  caudal  portion  remain 
as  the  paradidymis  and  vasa  aberrantia;  the  duct  persists  as  the  vas  epididy- 
midis,  vas  deferens,  and  ejaculatory  duct.  In  the  female  the  mesonephric  tu- 
bules disappear  for  the  most  part,  only  a  few  remaining  to  form  the  epoopho- 
ron  and  paroophoron,  while  the  duct  persists  in  part  as  Gartner's  canal. 

Each  kidney  begins  in  embryos  of  5  to  6  mm.  as  a  hollow  bud  on  the  dorsal 
side  of  each  mesonephric  duct  near  its  opening  into  the  gut.  This  bud  grows 
dorsally,  and  then  turns  cranially  in  the  mesoderm  between  the  vertebral 
column  and  the  mesonephros.  The  proximal  portion  remains  more  slender  as 
the  ureter,  while  the  distal  end  becomes  dilated  to  form  the  primitive  renal 
pelvis.  From  this  dilated  end  a  number  of  secondary  evaginations  grow  out 
to  form  the  papillary  ducts  and  straight  collecting  tubules. 

The  mesodermal  tissue  surrounding  the  outgrowths  from  the  primitive  renal 
pelvis  becomes  conden.scd  in  places  and  gives  ri.se  to  the  convoluted  portions  of  the 
uriniferous  tubules  and  to  Ilenle's  loops.  A  glomerulus  develops  in  connection 
with  the  distal  end  of  each  convoluted  tubule.  The  portion  of  each  tubule 
derived  from  the  mesodermal  tissue  unites  secondarily  at  the  arched  (junctional) 
tubule  with  the  portion  derived  from  the  renal  pelvis.  Thus  the  kidney  tubules 
arc  derived  in  j)art  directly  from  undifferentiated  me.sotlerm  (convoluted 
tubules  and  Ilenle's  loop.s)  and  in  part  from  an  outgrowth  from  tlie  mesonephric 
duct  (straight  collecting  tubules  and  papillary  ducts). 


378  THE  ORGANS 

During  foetal  life  the  kidneys  are  distinctly  lobulated,  but  after  birth  the 
surface  becomes  quite  smooth. 

The  genital  gland  on  each  side  appears  on  the  mesial  surface  of  the  meso- 
nephros  as  a  thickening  of  a  narrow  band  of  the  mesothelial  lining  of  the  body 
cavity.  The  cells  in  the  band  become  differentiated  into  two  kinds — small 
cuboidal  cells  which  stain  rather  intensely,  and  larger  spherical  cells  with  clearer 
cytoplasm  and  vesicular  nuclei.  The  latter  are  the  sex  cells  which  are  destined 
to  give  rise  to  the  ova  in  the  female  or  the  spermatozoa  in  the  male.  The 
whole  thickened  band  is  known  as  the  germinal  epithelium. 

The  cells  of  the  germinal  epithelium  increase  in  number  by  mitosis  and  soon 
become  differentiated  into  two  layers — a  superficial  layer  which  retains  its 
epithelial  character  and  contains  the  sex  cells,  and  a  deeper  layer  which  is  des- 
tined to  give  rise  in  part  to  the  stroma  of  the  genital  gland.  The  elevation 
caused  by  the  increased  number  of  cells  projects  into  the  body  cavity  as  the 
genital  ridge.  From  the  superficial  layer  containing  the  sex  cells  a  number  of 
plugs  or  columns  of  cells  grow  down  into  the  deeper  layer  carrying  some  of  the 
sex  cells  with  them.  Thus  far  (up  to  about  the  fifth  week)  the  changes  are 
common  to  both  sexes,  and  only  later  does  the  sex  differentiation  occur. 

After  about  the  fifth  week  certain  changes  occur  in  the  genital  ridge  which 
differ  accordingly  as  the  ridge  is  to  become  an  ovary  or  a  testicle.  In  the  case 
of  the  ovary  a  layer  of  loose  connective  tissue  grows  in  between  the  surface 
epithelium  and  the  cell  columns  or  plugs  mentioned  above.  The  cell  columns 
are  thus  pushed  farther  from  the  surface  and  constitute  the  medullary  cords. 
These  ultimately  disappear.  The  surface  epithelium  again  sends  plugs  of  cells 
(Pfliiger's  egg  cords)  down  into  the  underlying  tissue.  These  cords  are  made  up 
for  the  most  part  of  epithelial  cells  which  give  rise  to  the  follicular  cells,  but 
contain  also  a  considerable  number  of  sex  cells  (primitive  ova).  The  egg  cords 
then  become  broken  up  into  smaller  masses  each  of  which  contains  a  single 
primitive  ovum  (rarely  more)  and  constitutes  a  primitive  Graafian  follicle. 
The  sex  cell  grows  in  size  and  becomes  the  primary  oocyte  (and  finally  the  mature 
ovum),  while  the  epithelial  cells  around  it  give  rise  to  the  stratum  granulosum 
and  germ  hill  of  the  mature  Graafian  follicle.  During  these  processes  the  stroma 
also  increases  in  amount,  while  the  original  germinal  epithelium  becomes  reduced 
to  a  single  layer  of  cuboidal  cells.  The  formation  of  egg  cords  is  usually  com- 
pleted before  birth.     (See  also  p.  354.) 

In  the  case  of  the  testicle  a  layer  of  dense  connective  tissue,  the  tunica 
albuginea,  develops  between  the  germinal  epithelium  and  the  sex  cords.  The 
epithelium  becomes  reduced  to  a  single  layer  of  flat  cells.  The  sex  cords  which 
first  grew  into  the  underlying  tissue  and  which  contain  the  sex  cells,  are  destined 
to  give  rise  to  the  convoluted  seminiferous  tubules.  This  phase  of  development 
differs  from  that  in  the  ovary  inasmuch  as  in  the  latter  case  the  first  formed  sex 
cords  (medullary  cords)  disappear,  Pfliiger's  egg  cords  being  formed  later  and 
having  no  homologue  in  the  testicle.  The  sex  cords  of  the  testicle  become 
more  and  more  convoluted  and  the  sex  cells  (spermatogonia)  proliferate  rapidly. 
Beginning  after  birth  and  continuing  up  to  the  time  of  puberty,  lumina  appear 
in  the  sex  cords  and  they  thus  give  rise  to  the  convoluted  seminiferous  tubules. 
The  supporting  cells  (of  Sertoli)  are  probably  derived  from  the  undifferentiated 
epithelial  cells  of  the  sex  cords.     (See  also  p.  335.) 


THE  REPRODUCTIVE  SYSTEM  379 

TECHNIC 

(i)  A  human  uterus — if  possible  from  a  young  adult — or,  if  this  cannot  be  ob- 
tained, the  uterus  of  a  cat  or  dog,  is  cut  transversely  into  slices  about  i  cm.  thick 
and  fixed  in  Zenker's  fluid  (technic  9,  p.  8)  or  in  formalin- ]MiiIler's  fluid  (technic 
5,  p.  7).  For  topography  these  shces  are  cut  in  half  through  the  middle  of  the 
uterine  cavity  and  sections  made  through  the  entire  half  organ.  These  are  stained 
with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  21)  and  mounted  in  balsam. 
For  details  of  the  mucous  membrane,  cut  away  most  of  the  muscle  from  around 
the  half  sHce,  being  careful  not  to  touch  the  mucous  surface;  make  thin  sections, 
stain  with  haematoxjdin-eosin  (technic  i,  p.  20),  and  mount  in  balsam. 

(2)  Sections  of  the  cervix  may  be  prepared  in  the  same  manner  as  the 
preceding. 

(3)  Placental  tissue  may  be  cut  into  small  cubes  and  treated  with  the  same 
technic  (i). 

(4)  If  a  human  or  animal  uterus  with  the  placenta  in  situ  is  obtainable  it 
should  be  cut  into  thin  slices  and  fixed  in  formalin-Miiller's  fluid.  The  blocks 
of  tissue  should  be  so  arranged  that  sections  include  the  utero-placental  junc- 
tion. They  may  be  stained  with  haematoxylin-eosin  or  with  h«matoxylin-picro- 
acid-fuchsin  (see  above). 

(5)  Treat  pieces  of  the  human  vagina  according  to  technic  i,  p.  254. 

General  References  for  Further  Study 

Ballowitz:  Weitere  Beobachtungen  liber  den  feineren  Bau  der  Saugethier- 
Spermatozoen.     Zeit.  f.  wiss.  Zool.,  Bd.,  Hi,  189 1. 

Hertwig:  Lehrbuch  der  Entwickelungsgeschichte  des  ^Menschen  und  der 
Wirbelthiere,  Jena,  1896. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 

Nagel:  Das  menschhche  Ei.     Arch.  mik.  Anat.,  Bd.  xxxi,  1888. 

Ruckert:  Zur  Eireifung  der  Copepoden.  Anat.  Hefte,  I.  Abth.,  Bd.  iv, 
1894. 

Schaper:  Chapter  on  the  Placenta  in  Stohr's  Text-book  of  Histology,  5th  ed. 

Sobotta:  Ueber  die  Bildung  des  Corpus  luteum  bei  der  Maus.  Arch.  f. 
mik.  Anat.,  Bd.  xlvii,  1896. — Ueber  die  Bildung  des  Corpus  luteum  beim 
Kaninchen.     Anat.  Hefte,  I.  Abth.,  Bd.  viii,  1897. 


CHAPTER  X 
THE  SKIN  AND  ITS  APPENDAGES 

The  Skin 

The  skin  or  cutis  consists  of  two  parts:  (i)  The  derma,  corium, 
or  true  skin,  and  covering  this,  (2)  the  epidermis  or  cuticle.  The 
derma  is  a  connective-tissue  derivative  of  the  mesoderm,  the  epider- 
mis an  epithelial  derivative  of  the  ectoderm. 


•""•;\    .-f'!'^?'^. 


- —  d 


ws^.^ 


^a- 


ff 


CI-^Xj-  '--"  /^,lier' 


0 


Fig.  263. — -Vertical  Section  of  Thin  Skin,  Human.  X60.  (Technic  2,  p.  385. )'a, 
Epidermis;  h,  pars  papillaris  of  derma;  c,  papillas;  d,  pars  reticularis  of  derma;  e,  duct  of 
sweat  gland;  /,  sweat  gland;  g,  subcutaneous  fat. 

The  Derma. — This  is  divided  into  two  layers  which  blend 
without  distinct  demarcation.  The  deeper  is  known  as  the  pars 
reticularis,  the  more  superficial  as  the  pars  papillaris  (Fig.  263), 

The  -pars  reticularis  is  made  up  of  rather  coarse,  loosely  arranged 

380 


THE  SKIN  AND  ITS  APPENDAGES 


381 


white  and  elastic  fibres  with  connective-tissue  cells  in  varying  num- 
bers. The  fibres  run  for  the  most  part  parallel  to  the  surface  of  the 
skin. 

The  pars  papillaris  is  similar  in  structure  to  the  preceding,  but 
both  white  and  elastic  fibres  are  finer  and  more  closely  arranged. 
Externally  this  layer  is  marked  by  minute  folds  which  are  visible  to 
the  naked  eye,  and  can  be  seen  intersecting  one  another  and  enclos- 
ing small  irregular  areas  of  skin.  In  the  thick  skin  of  the  palms  and 
soles  these  furrows  are  close  together  and  parallel,  while  between 
them  are  long  corresponding  ridges.     In  addition  to  the  furrows  and 


A\ 


Fig.  264.— Thick  Vertical  Seclion  through  Skin  of  Finger  Tip.  (Merkel-Henle.") 
A,  Epidermis;  B,  derma;  C;  subcutis.  a,  Stratum  corneum;  b,  duct  of  sweat  gland;  c, 
stratum  lucidum;  d,  stratum  germinativum;  e,  papilla  of  derma;  /,  derma;  g,  blood- 
vessel; h,  sweat  gland;  /,  fat  lobule;  p,  sweat  pore. 


ridges  the  entire  surface  of  the  corium  is  beset  with  minute  papillae. 
These  vary  in  structure,  some  ending  in  a  single  point — simple  pa- 
pilla— others  in  several  points — compound  papilla;  some  containing 
blood-vessels — vascular  papilla;  others  containing  special  nerve 
termmiiiions— -nerve  papilla  (Fig.  265). 

Smooth  muscle  cells  occur  in  the  corium  in  connection  with  the 
sweat  glands.  In  the  skin  of  the  scrotum — tunica  dartos — and  of  the 
nipple,  the  smooth  muscle  cells  are  arranged  in  a  network  parallel  to 
the  surface.  In  the  face  and  neck  striated  muscle  fibres  penetrate 
the  corium. 

Beneath  the  corium  is  the  subcutaneous  tissue.     This  consists  of 


382  THE  ORGANS 

vertically  disposed  bands  of  connective  tissue — the  retinaculce  cutis — 
which  serve  to  unite  the  corium  to  the  underlying  structures  and 
enclose  fat  lobules.  In  some  parts  of  the  body  this  subcutaneous  fat 
forms  a  thick  layer — the  panniculus  adiposus. 

The  Epideemis. — This  is  composed  of  stratified  squamous 
epithelium.  In  the  comparatively  thin  skin  of  the  general  body  sur- 
face the  epidermis  is  divided  into  two  sublayers:  (i)  One  lying  just 
above  the  papillary  layer  of  the  derma,  and  known  as  the  stratum 


af^^SZ 


J>^ 


1  ?^'^-^.r^Jt^%^t  ^>. 


?  -S'.  ««,  fe^  ^If      ^l 


Fig.  265. — From  Vertical  Section  through  Skin  of  Human  Finger  Tip.  X200. 
(Schafer.)  a,  Stratum  corneum;  b,  stratum  lucidum;  c,  stratum  granulosum;  d,  stratum 
germinativum.  To  the  left  a  vascular  papilla;  to  the  right  a  nerve  papillalconta.mmg 
tactile  corpuscle. 

germinativum  (stratum  mucosum — stratum  Malpighii) ;  (2)  the  other 
constituting  the  superficial  layer  of  the  skin — the  horny  layer  or 
stratum  corneum.  In  the  thick  skin  of  the  palms  and  soles  two  ad- 
ditional layers  are  developed;  (3)  the  stratum  granulosum;  and  (4) 
the  stratum  lucidum  (Fig.  264). 

(i)  The  stratum  germinativum  consists  of  several  layers  of  cells, 
The  deepest  cells  are  columnar  and  form  a  single  layer  (stratum 
cylindricum) ,  which  rests  upon  a  basement  membrane  separating  it 


THE  SKIN  AND  ITS  APPENDAGES 


383 


from  the  derma.  The  membrane  and  cells  follow  the  elevations  and 
depressions  caused  by  the  papilla.  The  rest  of  the  stratum  germi- 
nativum  consists  of  large  polygonal  cells.  These  cells  have  well- 
developed  intercellular  bridges,  which  appear  as  spines  projecting  from 
the  surfaces  of  the  cells.  For  this 
reason  the  cells  are  sometimes  called 
"prickle''  cells,  and  the  layer,  the 
"stratum  spinosum."  The  spines 
cross  minute  spaces  between  the  cells, 
which  are  believed  to  communicate 
with  the  lymph  spaces  of  the  derma 
(Fig.  266,  c).  The  cells  of  the  stratum 
germinativum  are  usually  in  a  state 
of  active  mitosis. 

(2)  The  stratum  grannlosum  is  well 
developed  only  where  the  skin  is  thick. 
It  consists  of  from  one  to  three  layers 
of  flattened  polygonal  cells.  The 
protoplasm  of  these  cells  contains 
deeply  staining  granules — keratohya- 
line  granules — which  probably  repre- 
sent a  stage  in  the  formation  of  the 
horny  substance — keratin — of  the 
corneum  cells.  The  nuclei  of  these 
cells  always  show  degenerative 
changes,  and  there  is  reason  for  be- 
lieving that  this  karyolysis  is  closely 
associated  with  the  formation  of  the 
keratohyaline  granules  (Fig.  266,  b). 

(3)  The  stratum  lucidum  is  also 
best  developed  where  the  skin  is 
thickest.  It  consists  of  two  or  three 
layers  of  flat  clear  cells,  the  outlines  of 
which  are  frequently  so  indistinct  that 
the  layer  appears  homogeneous.  The 
transparency  of  the  cells  is  due  to  the 

presence  of  a  substance  known  as  elcidin,  and  derived  from  the 
keratohyaline  granules  of  the  stratum  granulosum  (Fig.  266,  a). 

(4)  The  stratum  corneum  varies  greatly  in  thickness,  reaching  its 
greatest  development  in  the  skin  of  the  i)ahns  and  soles.     The  cells 


**^^  '  ^  @  i 

r^^^ 


Vu,.  266. — F'rom  Vertical  Section 
through  Thick  Skin.  (Merkcl- 
Henle.)  </,  Stratum  lucidum;  b, 
stratum  granulosum;  c,  stratum 
germinativum,  showing  intercellular 
bridges. 


384  THE  ORGANS 

are  flattened  and  horny,  especially  near  the  surface.  Some  appear 
homogeneous,  others  have  a  lamellated  appearance.  They  contain 
pareleidin,  a  derivative  of  the  eleidin  of  the  stratum  lucidum.  Nuclei 
are  lost,  but  in  many  of  the  cells  can  be  seen  the  spaces  which  the 
nuclei  once  occupied.  Constant  desquamation  of  these  cells  goes  on, 
cells  from  the  deeper  layers  taking  their  place. 

The  color  of  the  skin  in  the  white  races  is  due  to  pigmentation  of 
the  deeper  layers  of  the  epidermis.  In  certain  parts  of  the  body  pig- 
mentation of  the  connective-tissue  cells  of  the  derma  also  occurs.  In 
the  dark  races  all  cells  of  the  epidermis  are  pigmented,  although  there  is 
less  pigment  in  the  surface  cells  than  in  the  cells  more  deeply  situated. 

Two  kinds  of  glands  occur  in  the  skin — sebaceous  glands  and 
sweat  glands. 

Sebaceous  Glands. ^ — These  are  usually  associated  with  the  hair 
follicles,  and  will  be  described  in  that  connection.  Sebaceous  glands 
unconnected  with  hair  occur  along  the  margin  of  the  lips,  in  the  glans 
and  prepuce  of  the  penis,  and  in  the  labia  minora. 

Sweat  Glands  {glandula  sudoriparse.) — These  are  found  through- 
out the  entire  skin  with  the  exception  of  the  margin  of  the  lips,  the 
inner  surface  of  the  prepuce,  and  the  glans  penis.  They  are  simple 
coiled  tubular  glands.  The  coiled  portion  of  the  gland  usually  Hes 
in  the  subcutis,  although  it  may  lie  wholly  or  partly  in  the  deeper 
portion  of  the  pars  reticularis.  The  excretory  duct  runs  a  quite 
straight  course  through  the  derma,  and  enters  the  epidermis  in  one  of 
the  depressions  between  the  papillae.  In  the  epidermis  the  duct 
takes  a  spiral  course  to  the  surface,  where  it  opens  into  a  minute  pit 
just  visible  to  the  naked  eye — the  sweat  pore  (Fig.  264,  p.) .  The  coiled 
portion  of  the  gland  is  Hned  with  a  simple  cuboidal  epithelium,  having 
a  granular  protoplasm.  In  the  smaller  glands  the  epithelium  rests 
directly  upon  the  basement  membrane.  In  the  larger  glands  a  longi- 
tudinal layer  of  smooth  muscle  cells  separates  the  glandular  epithe- 
lium from  the  basement  membrane.  The  walls  of  the  ducts  consist  of 
two  or  three  layers  of  cuboidal  epithehal  cells,  resting  upon  a  delicate 
basement  membrane,  outside  of  which  are  longitudinally  disposed 
connective-tissue  fibres.  On  reaching  the  horny  layer  the  epithehal 
wall  of  the  duct  ceases,  the  duct  consisting  of  a  mere  channel  through 
the  epithelium  (Fig.  264). 

TECHNIC 

(i)  Fix  the  volar  half  of  a  finger-tip  in  formalin-Miiller's  fluid  (technic  5,  p. 
7)  or  in  absolute  alcohol.     Curling  may  be  prevented  by  pinning  to  a  piece  of 


THE  SKIX  AXD  ITS  APPENDAGES 


385 


cork.  Sections  are  cut  transversely  to  the  ridges,  stained  with  ha^matoxylin-picro- 
acid-fuchsin  (technic  3,  p.  21),  and  mounted  in  balsam.  Thick  sections  should  be 
cut  for  the  study  of  the  coil  glands  with  their  ducts;  thin  sections  for  cellular 
details  of  the  layers. 

(2)  Prepare  in  the  same  manner  and  for  contrast  with  the  preceding,  sec- 
tions of  thin  skin  from  almost  any  part  of  the  body. 

(3)  Prepare  a  piece  of  negro  skin  in  the  same  manner  and  note  the  position  of 
the  pigment. 

The  Nails 

The  nails  are  modified  epidermis.  Each  nail  consists  of:  (a)  a 
body,  the  attached  uncovered  portion  of  the  nail;  {b)  a.  free  edge,  the 
anterior  unattached  extension  of  the  body;  (c)  the  nail  root,  the  pos- 
terior part  of  the  nail  which  Hes  under  the  skin  (Fig.  267). 


Fig.  jIj/.  Lwiigiludiniil  Secliun  ihrciUgh  Root  of  IIuiiKia  Xitil  and  Xuil  lied.  Xio. 
(Schaper.j  a,  Hody  of  nail;  b,  free  edge;  c,  root  of  nail;  d,  epidermis;  c,  ej)on3-chium; 
/,  stratum  germinativum  of  nail;  g,  folds  in  derma  of  nail  bed;  h,  bone  of  finger;  k, 
hy()onychium. 

The  nail  lies  upon  a  specially  modified  portion  of  the  cerium,  the 
nail  bed,  which  beneath  the  nail  root  and  somewhat  forward  of  the 
root  is  known  as  the  matrix.  The  nail  bed  is  bounded  on  either  side 
by  folds  of  skin,  the  nail  wall,  while  between  the  nail  wall  and  the 
nail  bed  is  a  furrow,  the  nail  groove  (Fig.  268). 

The  nail  bed  consists  of  corium.  Its  connective-tissue  fibres  arc 
arranged  partly  horizontal  to  the  long  axis  of  the  nail,  partly  in  a 

25 


386 


THE  ORGANS 


vertical  plane  extending  from  the  periosteum  to  the  nail.  Papillse 
are  not  present,  but  in  their  place  are  minute  longitudinal  ridges, 
which  begin  at  the  matrix  and,  increasing  in  height  as  they  pass  for- 


FiG.  268. — Transverse  Section  of  Nail  and  Nail  Bed.     (Rannie.)     «,  Nail;  a,  epidermis; 
^p,  nail  wall,  to  inner  side  of  which  is  the  nail  groove;  I,  folds  of  derma;  d,  nailbed. 

ward,  terminate  abruptly  at  the  end  of  the  nail  bed,  beyond  which  are 
the  usual  papillse  of  the  derma. 

The  nail  itself  consists  of  two  parts^- — an  outer  harder  part  or 


■'*?* 


4- 


^«^ 


Fig.  269. — Vertical  Transverse  Section  through.  Nail  Body.      X  2S0.     (Szymonowicz.) 
a,  Nail;  &,  stratum  germinativum;  c,  ridge  of  nail  bed;  d,  derma;  e,  blood-vessel. 

true  nail,  and  an  under  softer  part.  The  outer  portion  is  hard  and 
horny,  is  developed  from  the  stratum  lucidum,  and  consists  of  several 
layers  of  clear,  flat,  nucleated  cells.     These  layers  overlap  in  such  a 

^  Another  division  of  nail  and  nail  bed  considers  the  nail  as  composed  of  the  hard 
part  only,  the  soft  stratum  germinativum  being  considered  a  part  of  the  nail  bed. 


THE  SKIN  AXD  ITS  APPENDAGES  387 

manner  that  each  layer  extends  a  little  farther  forward  than  the  layer 
above.  The  under  softer  portion  of  the  nail  corresponds  to  the  stra- 
tum germinativum  of  the  skin  and,  like  the  latter,  consists  of  polygonal 
"prickle"  cells  and  a  stratum  cyHndricum  resting  upon  a  basement 
membrane.  In  the  matrix  where  the  process  of  nail  formation  is 
going  on,  this  layer  is  thicker  than  elsewhere  and  is  white  and  opaque 
from  the  presence  of  keratohyahn.  The  convex  anterior  margin  of 
this  area  can  be  seen  mth  the  naked  eye  and  is  known  as  the  lunula. 

At  the  junction  of  nail  and  skin,  in  the  nail  groove,  the  stratum 
corneum  extends  somewhat  over  the  nail  as  its  eponychium.  A  simi- 
lar extension  of  the  stratum  corneum  occurs  on  the  under  surface  of 
the  nail  where  the  nail  becomes  free  from  the  nail  bed.  This  is  known 
as  the  hyponychium  (Fig.  267). 

Growth  of  nail  takes  place  by  a  transformation  of  the  cells  of  the 
matrix  into  true  nail  cells.  In  this  process  the  outer  hard  layer  is 
pushed  forward  over  the  stratum  germinativum,  the  latter  remaining 
always  in  the  same  position. 

TECHNIC 

(i)  Remove  two  or  more  distal  phalanges  from  the  fingers  of  a  new-born  child 
and  fix  in  absolute  alcohol  or  in  formalin-Miiller's  fluid  (technic  5,  p.  7).  After 
fixing,  the  bone  should  be  carefully  removed.  Both  longitudinal  and  transverse 
sections  are  made,  stained  with  hsematoxyUn-picro-acid-fuchsin  (technic  3,  p.  21), 
and  mounted  in  balsam.  In  cutting  the  sections  it  is  usually  best  so  to  place  the 
block  that  the  knife  passes  through  volar  surface  first,  through  nail  last. 

(2)  The  cellular  elements  of  nail  do  not  show  well  in  sections.  For  demon- 
strating the  nail  cells,  boil  a  piece  of  nail  in  concentrated  potash  lye  or  warm  it  in 
strong  sulphuric  acid,  scrape  off  cells  from  the  softened  surface,  and  mount  in 
glycerin. 

The  Hair 

The  hair,  like  the  nail,  is  a  development  of  the  epidermis.  The 
hair  itself  consists  of  a  shaft,  that  portion  of  the  hair  which  projects 
above  the  skin,  and  a  root,  that  portion  embedded  within  the  skin.  At 
its  lower  end  the  root  presents  a  knob-like  expansion,  the  hair  bulb, 
in  the  under  surface  of  which  is  a  cup-like  depression,  which  receives 
an  extension  of  corium.  This  is  known  as  the  papilla.  Enclosing 
the  hair  root  is  the  hair  follicle. 

The  Hair. — This  is  composed  of  epithehal  cells  arranged  in  three 
layers,  which  from  within  outward  are  medulla,  cortex,  and  cuticle 
(Fig.  271). 

(i)  The  medulla  occupies  the  central  axis  of  the  hair.     It  is  absent 


388 


THE  ORGANS 


in  small  hairs,  and  in  the  large  hairs  does  not  extend  throughout  their 
entire  length.  It  is  from  i6  to  20/i  in  diameter,  and  consists  of  from 
two  to  four  layers  of  polygonal  or  cuboidal  cells  with  finely  granular, 
usually  pigmented  protoplasm  and  rudimentary  nuclei. 

(2)  The  cortex  makes  up  the  main 
bulk  of  the  hair  and  consists  of  several 
layers  of  long  spindle-shaped  cells,  the 
protoplasm  of  which  shows  distinct 
longitudinal  striations,  while  the 
nuclei  appear  atrophied.  As  these 
striations  give  the  hair  the  appear- 
ance of  being  composed  of  fibrillae, 
the  term  "cortical  fibres"  has  been 
applied  to  them.  In  colored  hair, 
pigment  granules  and  pigment  in 
solution  are  found  in  and  between  the 
cells  of  this  layer.  This  pigment  de- 
termines the  color  of  the  hair.  In 
the  root  the  cortical  cells  are  less 
flattened  than  in  the  shaft. 

(3)  The  cuticle  has  a  thickness  of 
about  ipL,  and  consists  of  clear  scale- 
like, non-nucleated  epithelial  cells. 
These  overlap  one  another  Uke 
shingles  on  a  roof,  giving  to  the  sur- 
face of  the  hair  a  serrated  appear- 
ance (Fig.  271). 

The  Hair  Follicle. — This  is 
also  a  modification  of  the  skin.  In 
the  formation  of  the  follicles  of  the 
finer  (lanugo)  hairs  the  epidermis 
alone  is  concerned.  The  follicles  of 
the  larger  hairs  contain  both  epi- 
dermal and  dermal  elements.  The  latter  form  the  connective-tissue 
follicle,  while  the  epidermis  forms  the  root  sheaths. 

(i)  The  root  sheath  consists  of  two  sub-layers — the  inner  root 
sheath  and  the  outer  root  sheath  (Figs.  272,  273  and  274). 

{a)  The  inner  root  sheath  consists  of  three  layers,  which  from 
within  outward  are  the  cuticle  of  the  root  sheath,  Huxley's  layer,  and 
Henle's  layer. 


wm'^ 


Fig.  270. — ^Longitudinal  Section 
of  Hair  and  its  Follicle  from  Vertical 
Section  of  Scalp.  (Ranvier.)  a, 
Shaft  of  hair;  b,  derma;  c,  arrector 
pili  muscle;  d,  sebaceous  gland;  e, 
outer  root  sheath;  /,  inner  root 
sheath;  g,  connective-ti  isue  follicle; 
h,  vitreous  membrane;  /,  hair  bulb; 
j,  papilla;  s,  epidermis. 


THE  SKIX  AND  ITS  APPENDAGES 


389 


The  cuticle  of  the  root  sheath  Hes  against  the  cuticle  of  the  hair 
and  is  similar  to  the  latter  in  structure.  It  consists  of  thin  scale-like 
overlapping  cells,  nucleated  in  the  deeper  parts  of  the  sheath,  non- 
nucleated  nearer  the  surface  (Figs.  272,  273  and  274,  c). 

Huxley^ s  layer  lies  immediately  outside  the  cuticle  of  the  root 
sheath,  constituting  the  middle  layer  of  the  inner  root  sheath.  It 
consists  of  about  two  rows  of  elongated  cells  with  slightly  granular 
protoplasm  containing  eleidin.  In  the  deeper  portion  of  the  root 
these  cells  contain  nuclei.  Nearer  the 
surface  the  nuclei  are  rudimentary  or 
absent  (Figs.  272,  273  and  274,  d). 

Henle's  layer  is  a  single  row  of  clear 
flat  cells.  In  the  bulb  these  cells  may 
contain  nuclei;  elsewhere  they  are  non- 
nucleated  (Fig.  274,  e). 

(b)  The  outer  root  sheath  is  derived 
from  the  stratum  germinativum  to 
which  it  corresponds  in  structure, 
Next  to  the  vitreous  membrane  is  a 
single  layer  of  columnar  cells  (stratum 
cylindricum) .  Inside  of  this  are  several 
layers  of  "prickle"  cells  (Figs.  272,  273 
and  274,/). 

(2)  The  connective-tissue  follicle  con- 
sists of  three  layers — an  inner  vitreous 
membrane,  a  middle  vascular  layer,  and 
an  outer  fibrous  layer. 

(a)  The  vitreous  or  hyaline  membrane  is  a  thin  homogeneous 
structure  of  the  nature  of  an  elastic  membrane.  It  lies  next  to  the 
outer  root  sheath  and  corresponds  to  the  basement  membrane  of  the 
derma  (Figs.  272,  273  and  274,  g). 

(b)  The  middle  or  vascular  layer  is  composed  of  fine  connective- 
tissue-fibrcs,  the  general  arrangement  of  which  is  circular.  Cellular 
elements  are  quite  abundant,  while  elastic  fibres  are,  as  a  rule,  absent. 
As  its  name  would  indicate,  this  layer  is  especially  rich  in  blood- 
vessels (Figs.  272,  273  and  274,  i). 

(c)  The  outer  or  fibrous  layer  consists  of  rather  coarse,  loosely 
woven  bundles  of  white-  fibres,  which  run  mainly  in  a  longitudinal 
direction.  Among  the.se  are  elastic  librcs  and  a  few  connective-tissue 
cells. 


Fig.  271. — Longitudinal  Section 
of  Hair.  X35C.  (KoUiker.)  a, 
Medulla;  b,  cortex;  c,  cuticle. 


390 


THE  ORGANS 


In  the  deeper  portion  of  the  root,  some  Uttle  distance  above  the 
bulb,  all  the  layers  of  the  hair  and  its  follicle  can  be  distinctly  seen. 
The  differentiation  of  the  layers  becomes  less  marked  as  one  passes 
in  either  direction.  At  about  the  level  of  the  entrance  of  the  ducts 
of  the  sebaceous  glands  (seep.  391)  the  inner  root  sheath  disappears, 
and  the  outer  root  sheath  passes  over  into  the  stratum  germinativum 
of  the  skin,  while  between  the  outer  root  sheath  (now  stratum  germi- 


FiG.  272. — ^Longitudinal  Section  of  Lower  End  of  Root  of  Hair,  including  Papilla. 
(Kolliker.)  a,  Root  of  hair;  b,  cuticle  of  hair;  c,  cuticle  of  root  sheath;  d,  Huxley's  layer 
of  inner  root  sheath;  e,  Henle's  layer  of  inner  root  sheath;/,  outer  root  sheath;  g,  vitreous 
membrane;/,  connective- tissue  follicle;  k,  bulb  of  hair;  p,  papilla. 


nativum)  and  the  hair  are  interposed  the  outer  layers  of  the  skin, 
stratum  granulosum  and  stratum  lucidum  when  present,  and  stra- 
tum corneum.  All  of  these  are  continuous  with  the  same  layers  of  the 
skin.  In  the  region  of  the  bulb  the  outer  root  sheath  first  becomes 
thinner,  then  disappears,  while  the  layers  of  the  inner  root  sheath 
retain  their  identity  until  the  neck  of  the  papilla  is  reached,  at  which 
point  the  different  layers  coalesce. 


THE  SKIN  AND  ITS  APPENDAGES 


391 


The  arrector  pili  muscle  (Fig.  270,  c)  is  a  narrow  band,  or  bands,  of 
smooth  muscle  connected  with  the  hair  follicle.  It  arises  from  the 
outer  layer  of  the  derma  on  the  side  toward  which  the  hair  slants,  and 
is  inserted  into  the  wall  of  the  follicle  at  the  junction  of  its  middle 
and  lower  thirds,  the  sebaceous  gland  being  usually  included  between 
the  muscle  and  the  hair  (see  below) .  The  contraction  of  the  muscle 
thus  tends  to  straighten  the  hair  and  to  compress  the  gland. 

The  sebaceous  glands  are  with  few  exceptions  connected  with  the 
hair  foUicles.     They  are  simple  or  branched  alveolar  glands.     The 


^     ...  ^ 

t    s 

I-  tij 


Fig.  273. — Transverse  Section  through  Root  of  Hair  and  Hair  Follicle,  (Kolliker.) 
o,  Hair;  b,  hair  cuticle;  c,  cuticle  of  root  sheath;  d,  Huxley's  layer;  e,  Henle's  layer;/, 
outer  root  sheath;  i,  connective-tissue  follicle. 


size  of  the  gland  bears  no  relation  to  the  size  of  the  hair,  the  largest 
glands  being  frequently  connected  with  the  smallest  hairs.  The 
glands  are  spherical  or  oval  in  shape  and  each  gland  is  enclosed  by  a 
connective-tissue  capsule  derived  from  the  follicle  or  from  the  derma. 
Beneath  the  capsule  is  a  basement  membrane  continuous  with  the 
vitreous  membrane  of  the  follicle.  The  wide  excretory  duct  empties 
into  the  upper  third  of  the  follicle  and  is  lined  with  stratified  squamous 
epithelium  continuous  with  the  outer  root  sheath  and  stratum  ger- 
minativum.     The  lower  end  of  the  duct  opens  into  several  simple  or 


392 


THE  ORGANS 


branched  alveoli,  at  the  mouths  of  which  the  epithelium  becomes 
reduced  to  a  single  layer  of  cuboidal  cells.  In  the  alveoli  themselves 
the  cells  are  spheroidal  or  polyhedral,  and  usually  fill  the  entire  al- 
veolus.    These  cells,  like  those  lining  the  duct,  are  derivatives  of 

the  outer  root  sheath.  The  secretion 
of  the  gland — an  oily  substance  called 
sebum — appears  to  be  the  direct  prod- 
uct of  disintegration  of  the  alveolar 
cells,  which  can  usually  be  seen  in  all 
stages  of  the  process  of  transformation 
of  the  cell  into  the  secretion  of  the 
gland.  The  most  peripheral  cells  show 
the  least  secretory  changes,  containing 
a  few  small  fat  droplets.  The  central 
cells  and  those  in  the  lumen  of  the 
duct  show  the  most  marked  changes, 
their  protoplasm  being  almost  wholly 
converted  into  fat,  their  nuclei 
shrunken  or  disintegrated  or  lost.  In 
the  middle  zone  are  cells  showing  in- 
termediary stages  in  the  process. 


xaaaSSi'-' 


/ 


/ 


Fig.  274. — From  Longitudinal 
Section  through  Hair  and  Hair 
FolUcle.  Enlarged  to  800  diameters. 
(Schafer.)  A,  Hair,  a,  Cortex  of 
hair;  b,  cuticle  of  hair.  B,  Inner 
sheath,  c,  Cuticle  of  root  sheath; 
d,  Huxley's  layer;  e,  Henle's  layer; 
/,  outer  root  sheath;  g,  vitreous 
membrane;  i,  connective-tissue  fol- 
licle; m,  fat  cells. 


Shedding  of  hair  occurs  in  most  mam- 
malia at  regularly  recurring  periods.  In 
man  there  is  a  constant  death  and  replace- 
ment of  hair.  In  a  hair  about  to  be  shed, 
the  bulb  becomes  cornified  and  splits  up  into 
a  number  of  fibres.  The  hair  next  becomes 
detached  from  the  papilla  and  from  the  root 
sheath  and  is  cast  off,  the  empty  root  sheaths 
collapsing  and  forming  a  cord  of  cells  between 
the  papilla  and  lower  end  of  the  shedding 
hair.  If  the  dead  hair  is  to  be  replaced  by 
a  new  one,  there  sooner  or  later  occurs  a 
proliferation  of  the  cells  of  the  outer  root 
sheath   in  the   region   of    the    old    papilla. 


From  this  "hair  germ"  the  new  hair  is 
formed  in  a  manner  similar  to  embryonal  hair  formation,  the  new  hair  growing 
upward  under  or  to  one  side  of  the  dead  hair,  which  it  finally  replaces. 

As  to  the  manner  in  which  growth  of  hair  takes  place,  two  views  are  held. 
According  to  one  of  these,  the  hair,  cuticle,  and  inner  root  sheath  are  replenished 
by  proliferation  of  the  epithelial  cells  surrounding  the  papilla.  These  parts 
thus  grow  from  below  toward  the  surface.  The  oldest  cells  of  the  outer  root- 
sheath,  on  the  other  hand,  lie  against  the  vitreous  membrane,  so  that  growth  of 


THE  SKIN  AND  ITS  APPENDAGES  393 

this  sheath  takes  place  from  without  inward.  According  to  the  second  view, 
the  various  parts  of  the  hair  and  its  foUicle  are  direct  derivatives  of  the  different 
layers  of  the  skin,  and  their  growth  takes  place  by  a  continuous  process  of  invag- 
ination. Thus  the  most  peripheral  cells  of  the  outer  root-sheath — stratum 
cyUndricum — pass  over  the  papilla  and  turn  upward  to  form  the  medulla  of 
the  hair;  the  deeper  cells — stratum  spinosum — of  the  outer  root-sheath  become 
continuous  with  the  cortex  of  the  hair;  the  stratum  lucidum,  with  the  sheath  of 
Henle,  which  turns  up  on  the  hair  as  its  cuticle;  Huxley's  layer,  with  the  cuticle 
of  the  inner  root-sheath.  According  to  this  view  growth  of  hair  is  accomplished 
by  continuous  growth  downward  from  the  surface,  and  turning  up  into  the 
hair,  of  these  layers. 

TECHNIC 

Pin  out  small  pieces  of  human  scalp  on  cork  and  fix  in  absolute  alcohol  or 
in  formaUn-Miiller's  fluid  (technic  5,  p.  7).  From  one  block  cut  sections  perpen- 
dicvilar  to  the  surface  of  the  scalp  and  in  the  long  axes  of  the  hair  and  follicles. 
From  a  second  block  cut  sections  at  right  angles  to  the  hair  follicles,  i.e.,  not  quite 
parallel  to  the  surface  of  the  scalp  but  a  Uttle  obliquely.  By  this  means  not 
only  are  transverse  sections  secured,  but  if  the  block  be  sufficiently  long  the  fol- 
licles are  cut  through  at  all  levels.  Sections  are  stained  with  haematoxylin- 
picro-acid-fuchsin  (technic  3,  p.  21)  and  mounted  in  balsam. 

Blood-vessels  of  the  skin.  From  the  larger  arteries  in  the  subcu- 
taneous tissue  branches  penetrate  the  pars  reticularis  of  the  derma, 
where  they  anastomose  to  form  cutaneous  networks.  The  latter  give 
ofif  branches,  which  pass  to  the  papillary  layer  of  the  derma  and  there 
form  a  second  series  of  networks,  the  subpapillary,  just  beneath  the 
papillai.  From  the  cutaneous  networks  arise  two  sets  of  capillaries, 
one  supplying  the  fat  lobules,  the  other  supplying  the  region  of  the 
sweat  glands.  From  the  subpapillary  networks  are  given  off  small 
arteries  which  break  up  into  capillary  networks  for  the  supply  of  the 
papillaj,  sebaceous  glands,  and  hair  follicles.  The  return  blood  from 
these  capillaries  first  enters  a  horizontal  plexus  of  veins  just  under 
the  papillae.  This  communicates  with  a  second  plexus  just  beneath 
the  first.  Small  veins  from  this  second  plexus  pass  alongside  the 
arteries  of  the  deeper  part  of  the  corium,  where  they  form  a  third 
plexus  with  larger,  more  irregular  meshes.  Into  this  plexus  pass 
most  of  the  veins  from  the  fat  lobules  and  sweat  glands,  although  one 
or  two  small  veins  from  the  sweat  glands  usually  follow  the  duct  and 
empty  into  the  subj)aj)illary  plexus.  The  blood  next  passes  into  a 
fourth  plexus  in  the  subcutaneous  tissue,  from  which  arise  veins  of 
considerable  size.     These  accompany  the  arteries. 


394  THE  ORGANS 

Small  arteries  from  the  plexuses  of  the  skin  and  subcutis  pass  to 
the  hair  follicle.  The  larger  arterioles  run  longitudinally  in  the  outer 
layer  of  the  follicle.  From  these  are  given  off  branches  which  form 
a  rich  plexus  of  small  arterioles  and  capillaries  in  the  vascular  layer 
of  the  folUcle.  Capillaries  from  this  plexus  also  pass  to  the  seba- 
ceous glands,  the  arrectores  pilorum  muscles,  and  the  papillae. 

The  lymphatics  of  the  skin.  These  begin  as  clefts  in  the  papillae, 
which  open  into  a  horizontal  network  of  lymph  capillaries  in  the 
pars  papillaris.  This  communicates  with  a  network  of  larger  lymph 
capillaries  with  wider  meshes  in  the  subcutaneous  tissue.  The  latter 
also  receives  lymph  capillaries  from  plexuses  which  surround  the  seba- 
ceous glands,  the  sweat  glands,  and  the  hair  follicles. 

The  nerves  of  the  skin.  These  are  mainly  sensory.  Efferent  sym- 
pathetic axones  supply  the  smooth  muscle  of  the  walls  of  the  blood- 
vessels, the  arrectores  pilorum,  and  secretory  fibres  to  the  sweat  glands. 
The  medullated  sensory  nerves  are  peripheral  processes  of  spinal  gang- 
lion cells.  The  larger  trunks  lie  in  the  sub  cutis,  giving  off  branches 
which  pass  to  the  corium,  where  they  form  a  rich  subpapillary  plexus 
of  both  medullated  and  non-medullated  fibres.  From  the  subcuta- 
neous nerve  trunks  and  from  the  subpapillary  plexus  are  given  off 
fibres  which  terminate  in  more  or  less  elaborate  special  nerve  end- 
ings (see  page  430).  Their  location  is  as  follows:  (i)  In  the  suhcutis: 
Vater-Pacinian  corpuscles,  the  corpuscles  of  Ruffini,  and  the  Golgi- 
Mazzoni  corpuscles  of  the  finger-tip.  The  first  two  forms  are  most 
numerous  in  the  palms  and  soles.  (2)  In  the  derma:  Tactile  corpuscles 
of  Meissner  and  Wagner.  These  are  found  in  the  papillae,  espe- 
cially of  the  finger  tip,  palm,  and  sole.  Krause's  end  bulbs — usually 
in  the  derma  just  beneath  the  papillae,  more  rarely  in  the  papillae 
themselves.  (3)  In  the  epithelium:  Free  nerve  endings  among  the 
epithelial  cells. 

Branches  of  the  cutaneous  nerves  supply  the  hair  follicles.  As  a 
rule  but  one  nerve  passes  to  each  follicle,  entering  it  just  below  the 
entrance  of  the  duct  of  the  sebaceous  gland.  As  it  enters  the  folHcle 
the  nerve  fibre  loses  its  medullary  sheath  and  divides  into  two 
branches,  which  further  subdivide  to  form  a  ring-Hke  plexus  of  fine 
fibres  encircHng  the  follicle.  From  this  ring,  small  varicose  fibrils 
run  for  a  short  distance  up  the  folHcle,  terminating  mainly  in  slight 
expansions  on  the  vitreous  membrane. 


THE  SKIN  AND  ITS  APPENDAGES  395 

TECHNIC 

For  the  study  of  the  blood-vessels  of  the  skin  inject  (technic,  p.  25)  the 
entire  hand  or  foot  of  a  new-born  child.  Examine  rather  thick  sections 
either  mounted  unstained  or  stained  only  with  eosin. 

Development  of  the  Skin,  Nails,  and  Hair 

The  epidermis  is,  as  already  noted,  of  ectodermic  origin.  It  consists  at  first 
of  a  single  layer  of  cuboidal  cells.  This  soon  differentiates  into  two  layers — 
an  outer,  the  future  stratum  corneum,  and  an  inner,  the  future  stratum  germ- 
inativum.  The  stratum  granulosum  and  stratum  lucidum  are  special  develop- 
ments of  the  stratum  germinativum.  The  corium  is  of  mesoblastic  origin.  It 
is  at  first  smooth,  the  papillae  being  a  secondary  development. 

The  nail  first  appears  as  a  thickening  of  the  stratum  lucidum.  This  spreads 
until  the  future  nail  bed  is  completely  covered.  During  development  the  stra- 
tum corneum  extends  completely  over  the  nail  as  its  eponychium.  During  the 
ninth  month  (intra-uterine)  the  nail  begins  to  grow  forward  free  from  its  bed 
and  the  eponychium  disappears,  except  as  already  noted. 

The  hair  also  develops  from  ectoderm.  It  first  appears  about  the  end  of  the 
third  fcetal  month  as  a  small  local  thickening  of  the  epidermis.  This  thicken- 
ing is  due  mainly  to  prohferation  of  the  cells  of  the  stratum  mucosum,  and  soon 
pushes  its  way  down  into  the  underlying  corium,  forming  a  long  slender  cord  of 
cells — the  hair  germ.  Differentiation  of  the  surrounding  connective  tissue 
of  the  corium  forms  the  follicle  wall,  while  an  invagination  of  this  connective 
tissue  into  the  lower  end  of  the  hair  germ  forms  the  papilla.  The  cells  of  the 
hair  germ  now  differentiate  into  two  layers:  a  central  core  the  middle  portion 
of  which  forms  the  hair,  while  the  peripheral  portion  forms  the  inner  root  sheath; 
and  an  outer  layer  which  becomes  the  outer  root  sheath.  The  sublayers  are 
formed  from  these  by  subsequent  differentiation.  The  hair  when  first  formed 
lies  wholly  beneath  the  surface  of  the  skin.  As  the  hair  reaches  the  surface 
its  pointed  extremity  pierces  the  surface  epithelium  to  become  the  hair  shaft 
(Fig.  275). 

The  sebaceous  gland  develops  as  an  outgrowth  from  the  outer  root  sheath. 
This  is  a  flask-shaped  and  at  first  solid  mass  of  cells,  which  later  differentiate  to 
form  the  ducts  and  alveoli  of  the  gland. 

The  sweat  glands  first  appear  as  solid  ingrowths  of  the  stratum  germina- 
tivum into  the  underlying  corium.  The  lower  end  of  the  ingrowth  becomes 
thickened  and  convoluted  to  form  the  coiled  portion  of  the  gland,  and  somewhat 
later  the  central  portion  becomes  channelled  out  to  form  the  lumen.  The 
muscle  tissue  of  the  sweat  glands,  which  lies  between  the  epithelium  and  the 
basement  membrane,  is  the  only  muscle  of  the  body  derived  from  the  ectoderm. 

The  Mammary  Gland 

The  mammary  gland  is  a  compound  alveolar  gland.  It  consists 
of  from  fifteen  to  twenty  lobes,  each  of  which  is  subdivided  into 
lobules.     The  gland  is  surrounded  by  a  layer  of  connective  tissue 


396 


THE  ORGANS 


/ 


Cr 


\    x<^ 


\         /s^s  "*  •*  C      , 


f1     IV 


-^^'z 


J^' 


\J^' 


r^*" 


' 'j^4''  AilSt     "^S- 'e       I 


iky-^ 


Fig  2  7^  —Five  stages  in  the  development  of  a  human  hair.  (Stohr.)  o,  PapiUa; 
^  arrecto/p'm  milcle;  cf  beginning  of  hai?  shaft;  i,  point  where  hair  shaft  gjo -  t Wg^ 
epidermis;  e,  anlage  of  sebaceous  gland;  /,  hair  germ;  g  hair  shaft;  ;2,  Henles  layer 
fnuSy's  layer;  \  cuticle  of  root  sheath;  I,  inner  root  sheat;  m,  outer  root  sheath  m 
tangential  section;  w.  outer  root  sheath;  o,  connective-tissue  folhcle. 


THE  SKIN  AND  ITS  APPENDAGES  397 

containing  more  or  less  fat.  From  this  periglandular  connective 
tissue  broad  septa  extend  into  the  gland,  separating  the  lobes  (inter- 
lobar septa).  From  the  latter  finer  connective-tissue  bands  pass  in 
between  the  lobules  (interlobular  septa).  From  the  interlobular 
septa  strands  of  connective  tissue  extend  into  the  lobule  where  they 
act  as  support  for  the  glandular  structures  proper.  An  excretory  duct 
passes  to  each  lobe  where  it  divides  into  a  number  of  smaller  ducts 
(lobular  ducts),  one  of  which  runs  to  each  lobule.     Within  the  latter 


■oS    ■     ■ 

ft' 


40- 


Fig.  276. — From  Section  of  Human  Inactive  Mammary  Gland.  X25.  (Technic 
I,  p.  401.)  Gland  composed  almost  wholly  of  connective  tissue;  few  scattered  groups 
of  tubules. 

the  lobular  duct  breaks  up  into  a  number  of  terminal  ducts,  which  in 
turn  open  into  groups  of  alveoli.  The  fifteen  to  twenty  main  excre- 
tory ducts  pass  through  the  nipple  and  open  on  its  surface.  At  the 
base  of  the  nipple  each  main  duct  presents  a  sac-like  dilatation,  the 
ampulla,  which  appears  to  act  as  a  reservoir  for  the  storage  of  the 
milk. 

Until  puberty  the  gland  continues  to  develop  alike  in  both  sexes, 
but  after  about  the  twelfth  year  the  male  gland  undergoes  retrogres- 
sive changes,  while  the  female  gland  continues  its  dcveloi)mcnt. 

The  inactive  mammary  gland,  by  which  is  meant  the  female 


398  THE  ORGANS 

gland  up  to  the  advent  of  the  first  pregnancy  and  between  periods  of 
lactation,  consists  mainly  of  connective  tissue  and  a  few  scattered 
groups  of  excretory  ducts  (Fig.  276).  Around  the  ends  of  some  of 
the  ducts  are  small  groups  of  collapsed  alveoli.  Both  ducts  and  alve- 
oli are  lined  with  a  low  columnar,  often  rather  flat  epithelium.  In 
some  cases  the  flat  cells  are  two  or  three  layers  thick,  forming  a  thin 
stratified  squamous  epithelium.  The  relative  amount  of  fat  and 
connective  tissue  varies  greatly,  some  inactive  mammae  consisting 
almost  wholly  of  fat  tissue. 


3"^  , 


-4^ 


y^^,  %'      ^<J      '\ 


Fig.    277. — From    Section    of    Human   Mammary   Gland   during  Lactation.     Xso. 
(Stohr.)     a,  Branch  of  excretory  duct;  b,  interlobular  connective  tissue;  c,  alveoli. 

The  Active  Mammary  Gland. — Throughout  pregnancy  the 
gland  undergoes  extensive  developmental  changes  and  becomes  func- 
tional at  about  the  time  of  birth  of  the  child.  The  microscopic 
appearance  of  the  active  gland  differs  greatly  from  that  of  the  inactive 
(Fig.  277).  There  is  a  marked  reduction  in  the  connective  tissue  of 
the  gland,  its  place  being  taken  by  newly  developed  ducts  and  alveoli. 
The  alveoli  are  spheroidal,  oval,  or  irregular  in  shape,  and  vary  con- 
siderably in  size.  The  alveoH  are  lined  by  a  single  layer  of  low  col- 
umnar or  cuboidal  epithehal  cells  which  rest  upon  a  homogeneous 
basement  membrane.  The  appearance  of  the  cells  differs  according 
to  their  secretory  conditions.     The  resting  cell  is  cuboidal  and  its 


THE  SKIX  AND  ITS  APPENDAGES 


399 


protoplasm  granular.  With  the  onset  of  secretion  the  cell  elongates, 
and  a  number  of  minute  fat  droplets  appear.  These  unite  to  form 
one  or  two  large  globules  of  fat  in  the  free  end  of  the  cell.  The  fat 
is  next  discharged  into  the  lumen  of  the  alveolus,  and  regeneration  of 
the  cell  takes  place  from  the  unchanged  basal  portion  (Fig.  279). 
As  to  the  number  of  times  a  cell  is  able  to  go  through  this  process 
of  secretion  and  repair  before  it  must  be  replaced  by  a  new  cell, 
nothing  definite  is  known.  Active  secretion  does  not  as  a  rule  take 
place  in  all  the  alveoli  of  a  lobule  at  the  same  time.     Each  lobule 


Fig.  278. — From  Section  ,of  Mammary  Gland  of  Guinea-pig  during  Lactation. 
Xsoo.  COsmic  acid.)  (Szymonowicz.)  a,  Basement  membrane;  6,  lumen  ot  ^alveolus; 
c,  tangential  section  of  alveolus;  d,  fat  globules. 

thus  contains  both  active  and  inactive  alveoli.  The  smallest  ducts 
are  lined  with  a  low  columnar  or  cuboidal  epithelium.  This  in- 
creases in  height  with  increase  in  the  diameter  of  the  duct  until 
in  the  largest  ducts  the  epithelium  is  of  the  high  columnar  type. 

The  secretion  of  the  gland  is  milk.  This  consists  microscopic- 
ally of  a  clear  fluid  or  plasma  in  which  are  suspended  the  milk 
globules.  The  latter  are  droplets  uf  fat  from  3  to  5/^  in  diameter, 
each  enclosed  in  a  thin  albuminous  membrane  which  prevents  the 
droplets  from  coalescing.  Cells,  probably  leucocytes,  containing  fat 
droplets  may  also  be  present.  In  the  secretion  of  the  gland  during 
the  later  months  of  pregnancy,  and  also  for  a  few  days  following  the 


400 


THE  ORGANS 


birth  of  the  child,  a  relatively  large  number  of  large  fat-containing 
leucocytes — colostrum  corpuscles — are  found. 

Blood-vessels. — These  enter  the  gland,  branch  and  ramify  in  the 
interlobar  and  interlobular  connective  tissue,  and  finally  terminate  in 
capillary  networks  among  the  alveoli  and  ducts.  From  the  capillaries 
arise  veins  which  accompany  the  arteries. 


sr. 


> 


_— -  g 


n  ^ 


A 


& 


\\C!!);|£^ 


-^yn  \£j 


v^ 


c 

Fig.  279. — A ,  Mammary  gland  cells — secreting  stage;  B,  same — excreting  stage;  the 
secretion  having  separated  from  the  cells;  C,  resting  stage;  w  =  nucleus.  ^  =  ergasto- 
plasm  filaments.     (Simon.) 

Lymphatics. — ^Lymph  capillaries  form  networks  among  the  alveoli 
and  terminal  ducts.  The  lymph  capillaries  empty  into  larger  lymph- 
atics in  the  connective  tissue.  These  in  turn  communicate  with 
several  lymph  vessels  which  convey  the  lymph  to  the  axillary  glands. 

Nerves. — Both  cerebro-spinal  and  sympathetic  nerves  supply  the 


THE  SKIX  AXD  ITS  APPENDAGES  401 

gland,  the  larger  trunks  follomng  the  interlobar  and  interlobular 
connective-tissue  septa.  The  nerve  terminals  break  up  into  plexuses 
which  surround  the  alvech  just  outside  their  basement  membranes. 
From  these  plexuses  dehcate  fibrils  have  been  described  passing 
through  the  basement  membrane  and  ending  between  the  secreting 
cells. 

Development. — The  development  of  the  mammary  gland  is  quite  similar 
to  the  development  of  the  sebaceous  glands.  The  gland  first  appears  as  a 
dipping  down  of  solid  cord-like  masses  of  cells  from  the  stratum  mucosum. 
The  alveoli  remain  rudimentary  until  the  advent  of  pregnancy.  After  lacta- 
tion the  alveoU  atrophy,  being  replaced  by  connective  tissue,  and  the  gland 
returns  to  the  resting  state.  After  the  menopause  a  permanent  atrophy  of 
the  gland  begins,  fat  and  connective  tissue  ultimately  almost  wholly  replacing 
the  glandular  elements. 

TECHNIC 

(i)  Fix  thin  sUces  of  an  inactive  mammary  gland  in  formalin-Muller's  fluid 
(technic  5,  p.  7).  Stain  sections  with  haimatoxylin-eosin  (technic  i,  p.  20),  and 
mount  in  balsam. 

(2)  Prepare  sections  of  an  active  mammary  gland,  as  in  preceding  technic  (i). 

(3)  Fix  very  thin  small  pieces  of  an  active  gland  in  one  per  cent,  aqueous 
solution  of  osmic  acid.  After  twenty-four  hours  wash  in  water  and  harden  in 
graded  alcohols.  Thin  sections  may  be  mounted  unstained,  or  after  slight  eosin 
stain,  in  glycerin. 

General  References  for  Fiirther  Study 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 
McMurrick:  Development  of  the  Human  body. 
Ranvier:  Traite  Technique  d'Histologie. 
Schafer:  Essentials  of  Histology. 

Spalteholz:  Die  Vertheilung  der  Blutgefasse  in  der  Haut.  Arch.  Anat.  u. 
Phys.,  Anat.  Abth.,  1893. 


CHAPTER  XI 

THE   THYREOID   AND   PARATHYREOID,   THE  PITUITARY 
BODY,  THE  PARAGANGLIA  AND  THE  ADRENAL. 

The  Thyreoid 

The  thyreoid  (Fig.  280)  is  a  ductless  structure  built  upon  the 
general  principle  of  a  compound  alveolar  gland.  There  are  usually 
two  lateral  lobes  connected  by  a  narrow  band  of  glandular  tissue, 
the  "isthmus."  Each  lobe  is  surrounded  by  a  connective-tissue 
capsule,  from  which  septa  pass  into  the  lobe,  subdividing  it  into 


:'?' 


w 


Fig.  280. — Section  of  Human  Thyreoid.     Most  of  the  alveoli  contain  colloid. 

lobules.  From  the  perilobular  connective  tissue  finer  strands  extend 
into  the  lobules,  separating  the  alveoli.  The  latter  are  spherical, 
oval,  or  irregular  in  shape.  They  vary  greatly  in  diameter  (40  to 
120/^)  and  are  as  a  rule  non-communicating.  At  birth  most  of  the 
alveoli  are  empty,  but  soon  become  more  or  less  filled  with  a  peculiar 
substance  known  as  "colloid."     The  alveoli  are  lined  with  a  ^single 

402 


THE  THYREOID  AXD  PARATHYREOID  403 

or  double  layer  of  cuboidal  epithelial  cells.     Two  types  of  cells  are 
recognized. 

One  of  these  is  actively  secreting  colloid  and  is  known  as  a  secreting 
or  colloid  cell.  The  other  contains  no  colloid  and  is  known  as  a 
resting  or  reserve  cell.  It  is  probable  that  their  names  indicate  the 
relation  of  these  cells  to  each  other  and  that  the  reserve  cell  ultimately 
becomes  a  colloid-secreting  cell. 

The  colloid  cell  appears  in  some  cases  simply  to  pour  out  its  colloid 
secretion  into  the  lumen,  after  which  it  may  assume  the  character  of  a 
resting  cell;  in  other  cases  the  cell  appears  to  be  completely  trans- 
formed into  colloid,  its  place  being  taken  by  proliferation  of  the  rest- 
ing cells.  In  certain  alveoli  which  are  much  distended  with  colloid 
the  lining  epithelium  is  flattened. 

That  the  thyreoid  exerts  a  decided  influence  upon  general  body  metabolism 
is  shown  by  the  symptoms  resuhing  from  congenital  absence  of  the  gland  (con- 
genital myxcedema  or  cretinism)  and  by  the  effects  of  complete  removal,  the 
latter  giving  rise  to  a  train  of  symptoms  known  as  the  "cachexia  strumipriva." 

The  blood  supply  of  the  thyreoid  is  extremely  rich,  the  vessels 
branching  and  anastomosing  in  the  connective  tissue  and  forming 
dense  capillary  networks  around  the  alveoli. 

Lymphatics  accompany  the  blood-vessels  in  the  connective  tissue. 

Nerves  are  mainly  non-medullated  fibres  which  form  plexuses 
around  the  blood-vessels  and  in  the  connective  tissue  surrounding 
the  alveoH.  Terminals  to  the  secreting  cells  end  in  club-like 
dilatations  against  the  bases  or  between  the  epithelial  cells.  A  few 
afferent  meduUated  fibres  are  found  in  the  plexuses  surrounding  the 
blood-vessels. 

Development. — The  thyreoid  originates  as  a  diverticulum  from  the  ento- 
derm of  the  primitive  pharynx.  It  first  appears  in  embryos  of  3  to  5  mm.  and 
grows  ventrally  into  the  mesoderm  of  the  ventral  wall  of  the  neck.  Here  it 
forms  a  mass  which  lies  transversely  across  the  neck.  It  is  composed  of  solid 
cords  of  cells  which  become  hollow  to  form  the  alveoli  of  the  gland.  At  first 
the  gland  is  connected  with  the  surface  by  the  thyreo-glossal  duct.  This  either 
disappears  entirely  or  is  represented  in  the  adult  by  such  rudimentary  structures 
as  the  so-called  prehyoid,  suprahyoid,  and  accessory  thyreoid  glands.  The 
gland  at  first  con.sists  of  solid  cords  of  cells.  Ingrowth  of  connective  tissue 
divides  these  into  groups  or  lobules,  and  at  the  same  time  breaks  up  the  long 
tubules  into  short  segments.  Dilatation  of  the  alveoli  occurs  with  the  formation 
of  colloid. 


404 


THE  ORGANS 


The  Parathyreoids 

These  are  small  ductless  glands  which  usually  lie  upon  the  posterior 
surface  of  the  lateral  lobes  of  the  thyreoid.  There  are  commonly 
two  pairs,  a  superior  and  an  inferior,  on  each  side.  The  number  is, 
however,  subject  to  variation.  Each  gland  is  from  6  to  8  mm.  long, 
about  half  that  in  breadth,  and  2  mm.  thick.  Small  groups  of  cells 
having  the  structure  of  the  parathyreoids  have  been  found  below  the 
thyreoid  and  within  the  thyreoid  and  thymus. 


t>^. 


^'  *  *'  "  •      '-^'Vti— ^.-^-<ss.'^- 


Fig.   281. — Section  of  Human  Parathyreoid;  showing  mainly    "clear," 

or  "chief"  cells.     (Pool.) 


"principal," 


The  parathyreoid  is  surrounded  by  a  thin  connective- tissue  capsule 
which  sends  a  variable  amount  of  connective  tissue  into  the  gland  as 
septa.  When  the  amount  is  considerable  the  gland  shows  a  sub- 
division into  lobules.  The  stroma  consists  largely  of  reticular  tis- 
sue and  is  very  vascular.  The  number  and  arrangement  of  the  cells 
vary.  The  gland  may  be  almost  wholly  cellular  with  very  little  con- 
nective tissue,  the  groups  of  cells  may  be  widely  separated  by  inter- 
stitial tissue,  or  there  may  be  any  intermediate  condition.  The  cells 
are  arranged  in  irregular  groups  or  cords  (Figs.  281,  282)  sometimes 
around  tubules,  sometimes  having  a  distinctly  alveolar  structure  (Fig. 


THE  THYREOID  AND  PARATHYREOID 


405 


283);  in  the  latter  case  colloid  may  be  present  in  the  lumen.  Colloid 
has  also  been  found  between,  and  colloid  and  glycogen  within,  the  cells. 
The  cells  themselves  are  spheroidal,  cuboidal  or  pyramidal,  with 
basal  nuclei.  The  appearance  of  the  cells  varies  suihciently  to  have 
caused  two  or  three  types  to  be  distinguished.  All,  however,  probably 
represent  different  functional  conditions  of  the  same  cell,  (i)  Chief 
or  clear  cells  (Fig.  281) .  These  are  the  more  numerous.  Their  bodies  are 
small  and  clear,  and  the  cytoplasm  does  not  stain  readily.     The  nuclei 


Fig.   282. — Section  of  Human  Parathyrcoid  showing  groups  of  oxyphilc  cells.     (Pool.) 


are  large  in  proportion  to  the  cell  and  are  clear  and  vesicular  with 
loosely  arranged  pale  chromatin  network.  (2)  Oxyphile  cells  (Fig. 
282).  These  are  larger,  their  cytoplasm  is  more  granular  and  takes 
a  strong  eosin  stain.  The  nucleus  is  small,  its  chromatin  network 
closely  arranged  and  takes  a  dark  stain.  Compact  groups  of  these 
cells  occur  especially  just  beneath  the  capsule.  They  are  also  found 
throughout  the  gland,  arranged  ^s  cords,  as  single  cells,  or  as  small 
grouf)S  among  the  clear  cells.     Intermediate  types  have  been  de- 


406 


THE  ORGANS 


scribed.     It  is  probable  that  the  clear  cells  represent  the  resting,  the 
granular  cells  the  active  secreting  condition  of  the  same  cell. 

The  parathyreoids  originate  as  epithelial  evaginations  from  the  third  and 
fourth  branchial  grooves,  and  develop  wholly  independently  of  the  thyreoid. 

The  powerful  influence  which  these  minute  organs  exert  is  shown  both  clinically 
and  experimentally.  Fatal  tetany,  resulting  from  the  earlier  operations  for 
complete  removal  of  the  thyreoids,  has  been  shown  by  animal  experimentation 
to  be  due  not  to  the  removal  of  the  thyreoids,  but  to  coincident  removal  of  the 
parathyreoids,  the  removal  of  the  latter  only,  in  animals,  giving  the  same  results.^ 


Fig.  283. — Section  of  Human  Parathyreoid,  showing  lumina  indicating  tubular  or 
tubulo-alveolar    structure.     (Pool.) 

TECHNIC 

The  thyreoid  and  parathyreoid  glands  are  best  fixed  in  formalin-Mxiller's  fluid. 
Sections  may  be  stained  with  haematoxylin-eosin  or  haematoxyhn-picro-acid- 
fuchsin  and  mounted  in  balsam. 


General  Reference  for  Further  Study 

Pool:  Tetany  Parathyreopriva.     Annals  of  Surgery,  October,  1907. 

^  For  much  of  the  description  of  the  parathyreoids  and  for  the  photograph   the 
writer  is  indebted  to  Dr.  Eugene  H.  Pool. 


PITUITARY  BODY  407 

The  Pituitary  Body 

The  Pituitary  Body  or  Hypophysis  Cerebri  consists  of  two  main 
lobes  which  are  totally  different  both  in  structure  and  in  origin. 
They  are  separated  by  a  cleft,  the  interglandular  cleft,  and  a  narrow 
strip  of  the  posterior  lobe  bordering  the  cleft  presents  a  different  struc- 
ture from  other  parts  of  the  gland.  This  has  been  designated  the 
pars  intermedia  (Fig.  284). 

The  Anterior  Lobe  {pars  anterior). — This  is  the  larger  of  the  two 
lobes  and  is  distinctly  glandular  in  character.  It  is  of  ectodermic 
origin,  developing  as  a  diverticulum  from  the  primitive  oral  cavity. 
Its  mode  of  development  is  that  of  a  compound  tubular  gland,  the 
single  primary  diverticulum  undergoing  repeated  division  to  form 
the  terminal  tub  ales.  The  original  diverticulum  ultimately  atrophies 
and  disappears,  leaving  the  gland  entirely  unconnected  with  the  sur- 
face. The  gland  is  enclosed  in  a  connective-tissue  capsule  from 
which  trabeculae  pass  into  the  organ  forming  its  framework.  The 
gland  cells  are  arranged  in  slightly  convoluted  tubules  and  rest  upon  a 
basement  membrane.  Between  the  tubules  is  a  vascular  connective 
tissue.  Some  of  the  gland  cells  are  small  cuboidal  cells  with  nuclei  at 
their  bases  and  a  clear  or  finely  granular  cytoplasm  (chief  cells). 
Others,  somewhat  less  numerous  than  the  preceding,  are  larger  and 
polygonal  with  centrally  placed  nuclei,  and  cytoplasm  containing 
coarse  basophile  granules  (chromophile  cells).  Cells  with  distinctly 
eosinophile  granules  may  also  be  present.  There  has  been  much 
controversy  as  to  whether  these  cells  are  fundamentally  different  or 
merely  represent  different  secretory  conditions  or  stages.  The  large 
variation  in  relative  number  of  the  different  forms,  and  the  occurrence 
of  cells  which  apparently  represent  intermediate  stages,  render  it 
probable  that  all  should  be  considered  as  merely  different  functional 
conditions  of  the  one  type  of  cell. 

As  in  all  ductless  glands,  the  blood  supply  is  rich,  the  vessels  being 
sinusoidal  in  character,  and  the  relations  of  capillaries  to  gland  cells 
is  extremely  intimate,  dense  networks  of  capillaries  surrounding  the 
alveoli  on  all  sides.  In  some  places  the  cells  are  so  placed  around  a 
capillary  as  to  resemble  the  relation  of  gland  cells  to  the  lumen. 

lite  Posterior  Lobe  (pars  posterior,  pars  nervosa). — This  like  the 
anterior  lobe  is  surrounded  by  a  connective-tissue  capsule  which 
sends  trabecuhe  into  its  substance.  In  the  human  adult  the  lobe 
consists  mainly  of  neuroglia  with  a  few  scattered  cells,  which  probably 


408 


THE  ORGANS 


represent  rudimentary  ganglion  cells  and  a  few  nerve  fibres.  In  the 
human  embryo,  and  in  many  adult  lower  animals,  the  nervous 
elements  are  much  more  prominent  and  more  definitely  arranged. 
Thus  Berkley  describes  the  posterior  lobe  of  the  pituitary  body  of  the 
dog  as  consisting  of  three  distinct  zones:  (i)  An  outer  zone  of  three 
or  four  layers  of  cells  resembfing  ependymal  cells,  connective- tissue 


/ 


Fig.  284. — Mesial  Sagittal  Section  through  Pituitary  Body  of  Five  Months  Human 
foetus.  (Herring.)  a,  Optic  chiasma;  h,  anterior  extension  of  pituitary  body;  c,  third 
ventricle  (infundibulum) ;  d,  pars  anterior;  e,  neck  or  isthmus  of  pars  nervosa  connecting 
it  with  bottom  of  infundibulum;  /,  epithelium  continuous  with  pars  intermedia  sur- 
rounding neck;  g,  interglandular  cleft;  h,  pars  nervosa  or  posterior. 


septa  from  the  capsule  separating  the  cells  into  irregular  groups.  (2) 
A  middle  zone  of  glandular  epithelium,  some  of  the  cells  of  which  are 
arranged  as  rather  indefinite  alveoli  which  may  contain  colloid.  This 
is  termed  the  pars  intermedia.  (3)  An  inner  layer  of  nerve  cells  and 
neuroglia  cells.  These  react  to  the  Golgi  stain,  the  nerve  cells  hav- 
ing axones  and  dendrites.  Most  of  the  axones  appeared  to  pass  in 
the  direction  of  the  infundibulum,  but  could  not  be  traced  into  the 
latter.     The  posterior  lobe  is  of  ectodermic  origin,  developing  as  a 


THE  PARAGANGLIA  409 

diverticulum  from  the  floor  of  the  third  ventricle.     The  remains  of 
the  diverticulum  constitute  the  infundibulum. 

The  so-called  middle  lobe  or  pars  intermedia  is  a  thin  layer  of  tissue 
which  covers  the  anterior  aspect  of  the  posterior  lobe  thus  lying 
between  it  and  the  interglandular  cleft.  It  develops  with  the  anterior 
lobe  and  like  it  consists  of  a  connective-tissue  framework  and  epithe- 
lial cells.  It  is  less  vascular,  however,  and  its  cells  are  smaller 
and  less  distinctly  granular.  The  cells  lining  the  cleft  are  columnar, 
thus  contrasting  with  the  flat  cells  of  the  opposite  wall.  Character- 
istic of  the  pars  intermedia  are  small  cyst-like  structures  which  con- 
tain colloid,  presenting  an  appearance  not  wholly  unlike  thyreoid, 
although  chemically  the  colloid  of  the  two  glands  is  not  identical. 
Lining  these  tiny  cysts  is  a  cuboidal  epithelium. 

The  nature  of  the  secretion,  its  function,  and  its  relation  to  the  various  kinds 
of  cells  have  been  subjects  of  much  controversy.  The  granules  within  the  cells 
undoubtedly  represent  an  intracellular  stage  of  the  secretion.  According  to 
some  investigators  each  type  of  cell  contributes  its  own  special  secretion  to  the 
general  secretion  of  the  gland.  According  to  most  authorities  the  different 
types  of  cells  represent  merely  different  stages  in  the  elaboration  of  the  secretion. 
Some  consider  the  colloid  a  special  secretion,  others  derive  it  from  the  cell 
granules  and  consider  it  as  possibly  representing  a  final  stage,  or  "  normal  de- 
generative condition  of  the  secretion." 

Pregnancy  apparently  induces  increased  activity  of  the  gland.  This  is  of 
interest  in  connection  with  the  clinical  use  of  the  extract  of  pituitary  body  for 
the  purpose  of  inducing  contractions  in  an  atonic  uterus  during  parturition  or 
for  the  control  of  post-partum  bleeding.  Pathological  conditions  of  the  pitu- 
itary, more  particularly  tumors  or  hyperplasia  of  the  anterior  lobe,  are  apparently 
associated  with  a  clinic3,l  condition  known  as  acromegaly  in  which  there  is 
marked  connective-tissue  hypertrophy,  especially  of  certain  bones.  The  con- 
nection between  acromegaly  and  lesions  of  the  pituitary  body  would  seem  to  be 
somewhat  similar  to  that  between  myxoedema  and  lesions  of  the  thyreoid.  Re- 
moval of  the  thyreoid  results  in  enlargement  of  the  pituitary  body,  especially 
in  increase  of  colloid.  Increase  of  colloid  has  also  been  reported  after  removal 
of  the  pancreas. 

The  Paraganglia 

Under  the  head  of  Paraganglia  are  grouped  certain  small  ductless 
glands  and  small  groups  of  cells  which  are  closely  associated  both 
anatomically  and  embryologically  with  the  sympathetic  .system. 
'J'hcy  include  the  carotid,  the  coccygeal,  and  lympanic  glands,  the  para- 
sympathetic organ  oj  Zuckerkandl,  and  the  medulla  of  the  adrenals. 
The  most  marked  characteristic  of  these   organs  aside  from  their 


410 


THE  ORGANS 


close  relation  to  the  sympathetic,  is  that  their  cells  take  a  yellowish 
brown  stain  when  placed  in  solutions  of  chromic  acid  or  chrome 
salts,  retaining  the  color  even  after  prolonged  washing  in  water.  For 
this  reason  the  cells  are  sometimes  referred  to  as  chromaffin  cells  and 
the  organs  as  chromaffin  organs} 

While  each  organ  has  its  own  peculiar  structure,  all  agree  in 
certain  general  features,  (i)  The  cells  are  polyhedral  and  have  a 
general  arrangement  into  cord-like  structures  rather  than  into  lobules; 
(2)  they  are  all  ductless  glands;  (3)  the  cells  lie  in  very  close  relation 


&Sts^ Septum. 


Trabecula  of 
cells  in  cross- 
section. 

Distended 
blood  capil- 
laries. 


Efferent  vein. 


Fig.  2S5. — Section  of  human  carotid  gland.     X  160.     (Schaper.) 

to  rich  capillary  networks  of  large  vessels,  some  of  which  resemble 
sinusoids  and  have  been  described  as  having  incomplete  walls,  the 
gland  cells  thus  being  in  direct  contact  with  the  blood  stream;  (4) 
unstained  the  cells  show  a  clear,  highly  refractive  cytoplasm,  but  con- 
tain secretion  granules  which  stain  yellowish  brown  with  chromic  acid 
and  chrome  salts,  red  with  safranine,  and  black  with  osmic  acid; 
(5)  all,  as  far  as  has  been  determined,  produce  an  internal  secretion 
which  passes  directly  into  the  blood  and  which  acts  as  a  regulator  of 
vascular  tone. 

The  Carotid  Glands. — These  are  two  small  ductless  glands,  each 
about  the  size  of  a  rice  grain,  which  lie  one  on  either  side  of  the 

^  Cells  containing  chromaffin  granules  have  also  been  described  as  occurring  in 
sympathetic  ganglia,  and  by  Rose  as  present  in  many  different  organs,  e.g.,  the  ovary, 
testicle,  blood-vessel  walls,  etc. 


THE  COCCYGEAL  GLAND 


411 


bifurcation  of  the  carotid  artery.  They  are  composed  of  a  vascular 
connective  tissue  supporting  spheroidal  groups  of  large  polyhedral 
epithelial  cells  with  poorly  marked  boundaries  and  closely  associated 
with  tufts  of  capillaries.  These  capillaries  are  of  large  diameter  and 
thin  walled,  and  have  been  described  as  sinusoidal  in  character. 
The  amount  of  connective  tissue  and  the  blood-vessels  increase  with 
age  at  the  expense  of  the  epithehal  elements.     This  probably  led  to 


vi 


^.^^ 


Fig,  286, — Section  through  coccygeal  gland.     (.Walker.) 
2.  epithelium;  3.  connective  tissue. 


I.  Blood  space; 


the  earlier  description  of  the  gland  as  a  vascular  or  glomerular  struc- 
ture. The  gland  cells  themselves  contain  chromaffin  granules  (p. 
410)  and  secrete  a  blood-pressure-raising  substance  apparently 
identical  with,  or  similar  in  nature  to,  the  secretion  of  the  adrenal 
Cp.  412). 

The  Coccygeal  Gland. — This  is  a  small  ductless  gland  which 
lies  just  in  front  of  the  apex  of  the  coccyx.  It  is  similar  in  structure 
to  the  preceding  but  has  its  cell  groui)s  more  irregularly  arranged 
(Fig.  286).  There  is  the  same  general  arrangement  of  gland  cells, 
the  same  relation  of  gland  cells  to  the  connective-tissue  framework 
and  to  large  sinusoidal  blood-vessels,  the  same  vascular  and  con- 


412 


THE  ORGANS 


nective  tissue  changes  with  age,  the  same  reaction  of  its  cells  to 
chrome  salts,  and  the  same  or  a  similar  secretion. 

The  tympanic  gland  and  the  organ  of  Zuckerkandl  are  small  col- 
lections of  chromaffin  cells,  the  former  lying  on  Jacobson's  nerve  in 

the  tympanic  canal,  the  latter  lying 
[^    in  the  retroperitoneal  tissue  at  about 
J       the  level  of  the  bifurcation  of  the 
abdominal  aorta. 


The  Adrenal 


The  adrenal  is  a  ductless  gland 
situated  on  the  upper  and  anterior 
surface  of  the  kidney.      It  is   sur- 

^  rounded  by  a  capsule  and  consists  of 
an  outer  zone  or  cortex  and  a  central 
portion  or  medulla.  The  cortex  and 
medulla  are  sharply  differentiated 
both  in  general  appearance  and  in 
histological  structure.  The  former 
is  of  rather  firm  consistency,  its  cells 
are  arranged  in  rows  with  the  blood- 
vessels between  them,  giving  the 
zone  a  striated  appearance.  Its  cells 
contain  fat  droplets  and  peculiar 
granules   known   as    lipoid  granules 

c  which  give  the  cortex  a  yellowish  tint. 
In  contrast  the  medulla  is  soft,  vas- 
cular, has  a  dark  reddish  appearance, 
and  its  cells  contain  granules  known 
as  chromaffin  or  phceochrome  granules. 
The    CAPSULE    (Fig.    287,    A)   is 

I     composed     of     fibrous     connective 

^'    tissue  and  smooth  muscle.     In  the 

c, 

outer  part  of  the  capsule  the  connec- 
tive tissue  is  loosely  arranged  and 
merges  with  the  surrounding  fatty  areolar  tissue.  The  inner  layer 
of  the  capsule  is  more  dense  and  forms  a  firm  investment  for  the 
underlying  glandular  tissue.  From  the  capsule  trabeculae  extend 
into  the  organ  forming  its  framework  and  outlining  compartments, 


Fig.     287. — Vertical     Section 
Adrenal.         (Merkel-Henle.) 
Capsule;    B,    cortex;    C,  medulla; 
glomerular  zone;  h,  fascicular  zone; 
reticular  zone;  v,  vein  in  medulla. 


THE  ADRENAL  413 

which  contain  the  glandular  epithelium.     This  connective  tissue  is 
reticular  in  character. 

The  CORTEX  (Fig  287,  B)  is  subdivided  into  three  layers  or 
zones:  (a)  A  narrow,  superficial  layer,  the  glomerular  zone;  {b)  a 
broad  middle  layer,  the  fascicular  zone;  and  (c)  a  narrow  deep  layer, 
the  reticular  zone.  The  names  of  the  layers  are  indicative  of  the 
shape  of  the  connective-tissue-enclosed  compartments  and  of  the 
contained  groups  of  gland  cells.  In  the  glomerular  zone  (Fig.  287,  a) 
the  high,  irregularly  columnar  epithelium  is  arranged  in  spherical  or 
oval  groups.  The  protoplasm  of  the  cells  is  granular,  contains  fat 
droplets,  and  their  nuclei  are  rich  in  chromatin.  In  the  fascicular 
zone  (Fig.  287,  h)  polyhedral  cells  are  arranged  in  long  columns  or 
fascicles.  The  cytoplasm  is  granular  and  usually  contains  many 
large  fat  droplets.  The  nuclei  contains  less  chromatin  than  those  in 
the  glomerular  zone.  The  appearance  which  the  protoplasm  of  the 
cells  richest  in  fat  presents  has  led  to  their  being  called  "spongi- 
oblasts. ' '  In  the  reticular  zone  (Fig.  287,  c)  similar  though  somewhat 
more  darkly  staining  cells,  containing  small  fat  droplets  or  sometimes 
no  fat  droplets,  form  a  coarse  reticulum  of  irregular  anastomosing 
cords. 

This  division  of  the  cortex  into  zones  is  more  distinct  in  some  of  the  lower 
animals.  It  does  not  indicate  any  fundamental  structural  or  functional  differ- 
ences. The  cells  in  the  different  zones  show  only  minor  variations  in  structure, 
the  characteristic  appearance  of  the  zone  depending  upon  the  arrangement  of 
the  cells  and  the  shape  of  the  connective-tissue  compartments.  According  to 
Gottschau  the  glomerular  zone  is  the  zone  in  which  active  formation  of  new 
cells  takes  place,  these  cells  gradually  passing  toward  the  medulla,  according  to 
some,  finally  completing'  their  history  as  medullary  cells.  Others  terminate 
the  life  history  of  these  cells  with  the  deepest  layer  of  the  cortex.  The  pigment 
formation  in  the  cells  of  the  reticular  zone  is  considered  by  some  a  degenerative, 
by  others  a  secretory  process.  Still  other  investigators  look  upon  the  deeper  cor- 
tical layers  as  the  site  of  most  active  cell  proliferation  and  an  indifferent  cell  here 
situated  as  giving  rise  on  the  one  hand  to  pigment  cells  and  on  the  other  to 
fat-producing  cells.  If  the  deeper  cells  are  the  older,  the  deeper  zone  would 
contain  the  more  mature  and  probably  the  more  functionally  active  cells,  and 
it  is  here  that  are  found  cells  crowded  with  fat  droplets  or  with  pigment  granules. 
The  former  begin,  according  to  some  investigators,  in  the  superficial  cell  as 
droplets  of  ordinary  fat,  which  becomes  changed  into  lecithin — an  easily  broken- 
down,  acid,  phosphorus-containing  fat  with  which  many  of  the  cells  of  the 
deeper  layers  arc  filled.  As  already  noted,  this  pigment  is  regarded  by  some  as 
the  last  stage  in  fat  formation,  by  others  as  an  entirely  independent  secretion. 
This  interrelation  of  cortical  and  medullary  cells  is  not,  however,  in  accord  with 
the  findings  of  embryology  or  of  comparative  anatomy  ([).  415). 


414  THE  ORGANS 

The  MEDULLA  (Fig.  287,  C)  consists  of  spherical  and  oval 
groups  and  cords  of  polygonal  cells.  After  alcohol  or  formalin  fixa- 
tion these  cells  take  a  paler  stain  than  those  of  the  cortex.  After 
fixation  in  solutions  containing  chromic  acid  or  chrome  salts  the  cells 
of  the  medulla  assume  a  peculiar  characteristic  deep  brown  color, 
which  cannot  be  removed  by  washing  in  water  and  which  is  due  to 
chromaffin  granules  which  they  contain  (p.  411).  The  chromaffin 
content  varies  in  different  animals  and  with  age.  Thus  while  in  the 
adult  human  the  chromaffin  reaction  is  strong,  little  or  no  re- 
action is  present  in  the  foetal  adrenal.  The  secretion  of  the  med- 
ullary part  of  the  adrenal  is  known  as  adrenalin,  apparently  the  ma- 
ture condition  of  the  intra-cellular  chromaffin  granules.  As  already 
noted  (p.  410)  it  is  probably  an  active  agent  in  the  regulation  of 
arterial  tension. 

Scattered  in  irregular  groups  among  the  chromaffin  cells  are  many 
sympathetic  ganglion  cells. 

Blood-vessels. — The  arteries  supplying  the  suprarenal  first  form 
a  poorly  defined  plexus  in  the  capsule.  From  this  are  given  off  three 
sets  of  vessels — one  to  the  capsule,  one  to  the  cortex,  and  one  to  the 
medulla.  The  first  set  breaks  up  into  a  network  of  capillaries,  which 
supply  the  capsule.  The  vessels  to  the  cortex  break  up  into  capillary 
networks,  the  shape  of  the  mesh  corresponding  to  the  arrangement  of 
the  connective  tissue  in  the  different  zones.  The  v^essels  to  the  me" 
dulla  pass  directly  through  the  cortex  without  branching  and  form 
dense  capillary  networks  among  the  groups  of  medullary  cells.  The  re- 
lations of  the  capillaries  to  these  glands  cells  are  extremely  intimate, 
especially  in  the  reticular  zone  and  medulla,  where  the  cells  in  many 
cases  immediately  surround  the  capillaries  in  much  the  same  manner 
as  the  glandular  cells  of  a  tubular  gland  surround  their  lumina.  From 
the  capillaries  of  both  cortex  and  medulla  small  veins  arise.  These 
unite  to  form  larger  veins  which  empty  into  one  or  two  main  veins 
situated  in  the  center  of  the  medulla. 

Ljmiphatics. — These  follow  in  general  the  course  of  the  blood- 
vessels. The  exact  distribution  of  the  suprarenal  lymph  system  has 
not  been  as  yet  satisfactorily  determined. 

Nerves. — The  nerve  supply  of  the  suprarenal  is  so  rich  and  the 
nerve  elements  of  the  gland  are  so  abundant  as  to  have  led  to  its 
classification  by  some  among  the  organs  of  the  nervous  system. 
Both  medullated  and  non-medullated  fibres — but  chiefly  the  latter 
—form  plexuses  in  the  capsule,  where  they  are  associated  with  groups 


THE  ADRENAL  415 

of  sympathetic  ganglion  cells.  From  the  capsular  plexuses  fine  fibres 
pass  into  the  cortex,  where  they  form  networks  around  the 
groups  of  cortical  cells.  The  nerve  terminals  of  the  cortex  appar- 
ently do  not  penetrate  the  groups  of  cells.  Bundles  of  nerve  fibres, 
larger  and  more  numerous  than  those  to  the  cortex,  pass  through  the 
cortex  to  the  medulla.  Here  they  form  unusually  dense  plexuses 
of  fibres,  which  not  only  surround  the  groups  of  cells,  but  penetrate 
the  groups  and  surround  the  individual  cells.  Associated  with  the 
plexuses  of  the  medulla,  less  commonly  of  the  cortex,  are  numerous 
conspicuous  groups  of  sympathetic  ganglion  cells. 

Development. — The  cortex  and  medulla  have  entirely  different  develop- 
mental histories.  In  the  lower  vertebrates  (fishes)  the  two  parts  of  the  gland 
continue  separate  throughout  life.  In  the  ascending  mammalian  scale,  the  two 
parts  become  more  and  more  closely  united  until  in  mammals  they  form  a  single 
organ.  The  cortex  develops  from  mesoderm,  first  appearing  in  embryos  of 
about  five  to  six  mm.  At  about  the  level  of  the  cephalic  third  of  the  mesone- 
phros  the  mesothelium  sends  outgrowths  into  the  mesenchyme.  These  out- 
growths soon  lose  their  connection  with  the  main  mass  of  mesothelium  and  con- 
stitute the  anlage  of  the  suprarenal  cortex.  The  medulla  has  an  entirely  inde- 
pendent origin,  being  derived  from  ectoderm,  as  part  of  the  peripheral  sym- 
pathetic nervous  system.  The  cells  of  some  of  the  sympathetic  ganglia  differ- 
entiate into  sympathoblasts  and  phceochromoblasts,  which  give  rise  to  the  sym- 
pathetic cells  and  chromaffin  cells  respectively.  These  cells  soon  separate  from 
their  ganglia  of  origin  and  come  to  lie  first  near,  then  within,  the  developing 
cortex,  thus  forming  the  medulla. 

General  References  for  Further  Study 

Flint:  The  Blood-vessels,  Angiogenesis,  Organogenesis,  Reticulum  and 
Histology  of  the  Adrenal.  Contributions  to  the  Science  of  Medicine,  Johns 
Hopkins  Press,  1900. 

Pfaundler:  zur  Anatomic  der  Nebenniere.     Anzeiger  Akad.  Wicn,  29,  1892. 

Nagel:  Ueber  die  Entwickelung  des  Urogenitalsystem  des  Menschen. 
Arch.  f.  Mik.  Anat.,  Bd.  xxxiv. 

Stohr:  Lchrbuch  der  Histologic  B.  15th  Ed. 

Prenant:  Traite  d'HistoIogie. 


CHAPTER  XII 

THE  NERVOUS  SYSTEM 

The  nervous  mechanism  in  man  consists  of  two  distinct  though 
associated  systems,  the  cerebrospinal  nervous  system  and  the  sympa- 
thetic nervous  system.  Each  of  these  systems  is  composed  of  a  central 
portion  which  is  its  center  of  nervous  activity,  and  of  a  peripheral 
portion  which  serves  to  place  the  center  in  connection  with  the  organs 
which  it  controls.  In  the  cerebro-spinal  system  the  central  portion  is 
known  as  the  central  nervous  system  and  consists  of  the  cerebro-spinal 
axis,  or  brain  and  spinal  cord.  The  peripheral  portion  is  formed  by 
the  cranial  and  spinal  nerves.  The  central  portion  of  the  sympa- 
thetic system  consists  of  a  series  of  ganglia  from  which  the  sympa- 
thetic nerves  take  origin.  These  latter  constitute  its  peripheral  por- 
tion. The  whole  sympathetic  system  is  usually,  however,  included 
under  the  peripheral  nervous  system  as  opposed  to  the  brain  and 
spinal  cord  or  central  nervous  system. 

HISTOLOGICAL  DEVELOPMENT  AND  GENERAL 
STRUCTURE 

The  beginning  differentiation  of  the  nervous  system  appears  very 
early  in  embryonic  life.  It  is  first  indicated  by  a  longitudinal  median 
thickening  of  the  outer  embryonic  layer  or  ectoderm,  to  form  the 
neural  plate.  The  sides  of  the  plate  become  elevated  to  form  the 
neural  folds,  leaving  between  them  the  neural  groove.  By  the  dorsal 
union  of  these  folds  the  neural  groove  is  converted  into  the  neural 
tube.  The  lumen  of  the  neural  tube  corresponds  to  the  central  canal 
of  the  cord  and  the  ventricles  of  the  brain  in  the  adult,  and  from  the  ec- 
toderrriic  cells  which  form  the  walls  of  this  tube  practically  the  entire 
nervous  system  is  developed.  The  caudal  portion  of  the  tube  is  of 
nearly  uniform  diameter — the  spinal  cord.  At  the  cephalic  end,  the 
neural  plate,  even  before  its  closure,  is  wider  and  forms,  when  closed, 
an  expanded  portion  of  the  tube,  the  brain.  In  their  further  develop- 
ment, the  walls  of  the  brain  form  three  expansions — the  three  brain 
"vesicles"  known  as  the  forebrain  (prosencephalon),  midbrain  {mes- 

416 


THE  NERVOUS  SYSTEM  417 

enceplmlon),  and  hindbrain  {rhombencephalon) .  In  the  forebrain  two 
main  divisions  are  usually  distinguished,  the  endbrain  {telencephalon) 
and  the  intcrbrain  {diencephalon).  The  basal  part  of  the  endbrain 
forms  the  corpora  striata  and  rhinencephalon,  while  the  dorsal  part  ex- 
pands into  the  pallium  {cerebral  hemispheres).  In  the  interbrain  may 
be  distinguished  a  dorsal  part,  the  epithalamus;  a  middle  (largest) 
part,  the  thalamus;  and  a  ventral  expansion,  the  hypothalamus. 
In  the  midbrain  the  basal  part  becomes  the  tegmentum,  and  the  dor- 
sal part  expands  into  the  corpora  quadrigemina  or  inferior  and  superior 
colliculi.  The  narrower  part,  connecting  midbrain  and  hindbrain,  is 
the  isthmus.  The  basal  part  of  the  hindbrain  forms  the  medulla  ob- 
longata and  part  of  the  dorsal  wall  expands  into  the  cerebellum.  In 
the  later  development  of  the  brain,  the  pallium,  and  with  it  parts 
of  the  cerebellum,  becomes  enormously  enlarged  and  structures  are 
formed  constituting  connections  between  the  pallium  and  the  rest  of 
the  brain.  The  most  massive  of  these  are  the  pes  pedmiculi,  added 
ventrally  to  the  thalamus  and  midbrain;  the  pons  Varolii,  added 
ventrally  to  part  of  the  midbrain,  isthmus  and  part  of  the  hind- 
brain; and  the  pyramids,  added  ventrally  to  the  medulla.  The 
basal  part  of  the  mid-  and  hindbrain,  thus  covered  ventrally  by  the 
pes  and  pons,  is  the  tegmentum.  Other  portions  of  the  dorsal  walls 
of  the  forebrain  and  hindbrain  form  thin-walled  expansions  which, 
together  with  vascular  mesodermic  coverings,  are  the  chorioid  plexuses 
of  the  lateral,  third,  and  fourth  ventricles.  The  cavities  of  the  cere- 
bral hemispheres  are  the  lateral  ventricles;  the  cavity  of  the  interbrain 
is  the  third  ventricle;  that  of  the  midbrain  is  the  iter  or  aqucBductus 
Sylvii;  that  of  the  hindbrain  is  the  fourth  ventricle. 

The  wall  of  the  neural  tube  is  at  lirst  composed  of  a  single  layer  of 
epithelial  cells.  By  proliferation  of  these  cells  the  epithelium  soon 
becomes  many-layered,  and  forms  a  syncytium — the  myelospongium 
of  His — although  some  of  the  original  epithelial  cells  appear  to  extend 
through  the  entire  thickness  of  the  wall. 

Some  of  the  syncytial  cells  which  extend  through  the  entire  thick- 
ness of  the  wall  of  the  neural  tul^e  (spongioblasts  of  His)  increase  in 
length  as  the  wall  increases  in  thickness.  The  inner  ends  of  these 
cells  form  the  lining  of  the  tube,  while  other  j)arts  of  the  cells  between 
the  lumen  and  the  surface  lend  to  collapse,  forming  cord-like  struc- 
tures. The  outer  ends  of  the  cells,  on  the  other  hand,  become  per- 
forated and  unite  to  form  a  thick  network — the  marginal  veil  of  His. 
Of  these  cells,  some  retain  this  position,  with  nuclei  near  the  lumen, 

27 


418  THE  ORGANS 

in  the  adult  and  are  known  as  ependymal  cells;  others  move  away 
from  the  central  canal  and  become  neuroglia  cells. 

Still  other  of  the  cells  of  the  neural  tube  are  destined  to  become 
neurones,  and  as  such  are  known  as  neuroblasts.  From  the  neuro- 
blast a  neurofibrillated  process  grows  out — the  future  axone.  Den- 
drites which  at  this  stage  are  absent  develop  later  in  a  similar  manner, 
i.e.,  by  extensions  of  the  cell  protoplasm.^  The  neuroblasts  soon 
leave  their  original  position  near  the  lumpen  and  pass  outward  along 
the  spaces  between  the  elongated  ependymal  cells,  but  their  bodies 
do  not  usually  penetrate  the  marginal  veil.  Some  may,  however, 
pass  through  and  even  leave  the  neural  tube  along  with  the  efferent 
roots.  The  axones  of  many  neuroblasts  located  in  the  ventral  part 
of  the  neural  tube  pierce  the  marginal  veil  and  leave  the  neural  tube 
as  the  efferent  root  fibres.  These  nerve  cells  together  with  many  of 
the  sympathetic  neurones  (see  below)  are  the  efferent  peripheral  neu- 
rones. Their  axones  pass  to  sympathetic  ganglia  or  to  various  struc- 
tures (muscles,  glandular  epithelia)  the  activities  of  which  they  affect. 
Such  structures  may  be  collectively  termed  effectors.  The  axones  of 
other  neuroblasts  do  not  completely  pierce  the  marginal  veil,  but  are 
directed  upward  and  downward  within  it,  thus  forming  fibres  con- 
necting various  parts  of  the  central  nervous  system.  Axones  of  still 
other  neuroblasts,  especially  in  suprasegmental  structures  (see  p. 
420) ,  are  directed  toward  the  lumen.  All  such  neurones  whose  axones 
do  not  leave  the  neural  tube  may  be  termed  intermediate  or  central 
neurones,  as  distinguished  from  the  peripheral  neurones:  inter- 
mediate, because  they  serve  as  intermediate  links  connecting,  within 
the  central  nervous  system,  the  terminations  of  the  efferent  per- 
ipheral neurones  (see  below)  with  the  bodies  of  the  efferent  peripheral 
neurones;  central,  because  they  are  confined  to  the  central  nervous 
system.  Later  becoming  meduUated,  their  axones  constitute  the 
great  majority  of  the  fibres  of  the  white  matter  of  the  central  nervous 
system. 

During  the  closure  of  the  neural  groove,  groups  of  cells  from  the 
crest  of  each  neural  fold  become  separated  from  the  rest  of  the  de- 
veloping nervous  system.  Some  of  these  cells  form  the  cerebrospinal 
ganglia,  while,  according  to  most  authorities,  others  migrate  still 
further  from  the  neural  tube  and  form  the  various  sympathetic  ganglia. 
Some  cells  (neuroblasts)  develop  into  the  nerve  cells  of  the  cerebro- 

1  According  to  other  views,  other  cells  may  participate  in  the  formation  of  the 
axone,  and  the  dendrites  may  anastomose  with  other  neuroblasts  (see  Chap.  VI)., 


THE  NERVOUS  SYSTEM  419 

spinal  and  sympathetic  ganglia.  Others  form,  according  to  some 
authorities,  enveloping  cells,  such  as  the  capsule  cells  around  the 
ganglion  cell  bodies  and  the  neurilemma  cells  around  the  peripheral 
nerve  fibres.  These  latter  would  thus  correspond  to  the  neuroglia 
cells  of  the  central  nervous  system.  The  majority  of  the 
neuroblasts  of  the  cerebro-spinal  ganglia  develop  two  processes: 
peripheral  processes  {afferent  nerve  fibres)  to  various  structures  (re- 
ceptors) which  receive  stimuli;  and  central  processes,  forming  the 
afferent  roots  and  passing  into  the  central  nervous  system  where  they 
usually  bifurcate  and  form  longitudinal  ascending  and  descending 
arms.  These  cells  are  at  first  bipolar,  later  the  cell  body  withdraws 
from  the  two  processes  and  thus  assumes  the  adult  unipolar  con- 
dition (see  page  427).  Other  processes  may  also  appear.  Many 
of  the  neuroblasts  of  the  sympathetic  ganglia  develop  dendrites  and 
axones  while  others  form  branching  cells  in  which  the  two  kinds  of 
processes  cannot  be  easily  distinguished.  Sympathetic  cells  are 
also  derived  from  cells  which  migrate  from  the  neural  tube  along  the 
efferent  root  (p.  418). 

The  cerebro-spinal  ganghonic  neurones,  together  with  some  sym- 
pathetic neurones,  certain  neurones  in  the  olfactory  mucous  mem- 
brane, retina,  and  possibly  midbrain  roof,  constitute  the  afferent  per- 
ipheral neurones  of  the  entire  nervous  system.  Most  of  the  sympa- 
thetic neurones  are  efferent.  The  peripheral  processes  of  the  afferent 
peripheral  neurones,  the  axones  of  the  efferent  peripheral  neurones 
after  they  have  emerged  from  the  central  nervous  system,  and  the 
axones  of  the  sympathetic  ganglion  cells,  together  with  all  their 
sheaths  and  connective-tissue  investments,  form  the  peripheral 
nerves.  The  bodies  of  the  afferent  peripheral  neurones  and  sym- 
pathetic neurones  form  groups  known  as  ganglia.  The  peripheral 
neurones  are  arranged  segfnentally,  as  shown  by  the  series  of  ganglia 
and  nerves. 

The  sympathetic  neurones  and  those  cerebro-spinal  neurones 
which  innervate  sympathetic  ganglia,  viscera,  glands,  blood-vessels, 
and  smooth  and  heart  muscle  are  peripheral  visceral  or  splanchnic 
neurones.  Those  cranial  nerve  neurones  which  innervate  the  striated 
voluntary  muscles  of  jaw,  ear,  face,  pharynx,  and  larynx  (branchio- 
motor)  are  usually  also  classed  as  splanchnic.  The  remainder  of 
the  cerebro-spinal  peripheral  neurones  are  peripheral  ^owa^^c  neurones. 

From  the  foregoing  it  will  be  seen  that  all  the  neurones  of  the 
nervous  system  fall  into  two  categories:     I.  Peripheral  neurones,  a 


420  THE  ORGANS 

part  of  whose  processes,  at  least,  lie  outside  the  central  nervous  sys- 
tem, forming  the  peripheral  nerves.  II.  Central  or  intermediate 
neurones.  These  lie  entirely  within  the  central  nervous  system. 
The  peripheral  neurones  may  be  classified  as  follows:  A.  Afferent 
peripheral  (all  the  neurone  bodies  located  outside  the  central  nervous 
system,  except  possibly  some  in  midbrain  roof).  The  afferent 
peripheral  neurones  are  (i)  the  cerebro-spinal  ganglion  cells,  which 
may  be  {a)  somatic,  {h)  splanchnic;  (2)  cells  in  olfactory  membrane, 
retina,  and  possibly  midbrain;  (3)  some  sympathetic  neurones 
(splanchnic).  'B.  Efferent  peripheral  YieuronQs.  These  are  (i)  cerebro- 
spinal (neurone  bodies  located  in  ventral  part  of  central  nervous 
system),  {a)  somatic  (to  voluntary  striated  muscles  except  (c)),  {h) 
splanchnic  (sending  axones  to  sympathetic  ganglia),  (c)  splanchnic  to 
voluntary  striated  branchiomotor  muscles  (p.  419);  (2)  sympathetic 
(splanchnic,  bodies  in  sympathetic  ganglia,  sending  axones  to  smooth 
muscle,  heart  muscle  and  glands) . 

In  the  central  nervous  system  the  bodies  and  dendrites  of  the 
neurones  are  usually  aggregated  within  certain  localities  which,  on 
account  of  their  appearance  when  examined  in  fresh  condition,  are 
collectively  termed  the  gray  matter  (substantia  grisea).  The  gray 
matter  also  contains,  of  course,  the  beginnings  and  endings  of  the 
nerve  fibres.  The  parts  of  the  nervous  system  where  the  bodies 
and  dendrites  are  absent  and  which  are  composed  (exclusive  of  the 
neuroglia,  blood-vessels,  etc.)  of  the  medullated  nerve  fibers  are 
collectively  termed  the  white  matter  (substantia  alba). 

The  central  nervous  system  may  be  divided  into  a  segmental  part 
and  certain  suprasegmental  parts.  The  former  is  in  more  immediate 
relation  with  the  peripheral  (segmental)  nerves.  It  comprises  the 
spinal  cord  and  basal  part  of  the  brain  (segmental  brain).  It  con- 
tains all  the  bodies  of  the  efferent  cerebro-spinal  neurones  and 
practically  all  the  terminations  of  the  central  processes  (afferent 
root  fibres)  of  the  afferent  peripheral  neurones.  In  it  the  gray  matter 
is  internal,  as  a  rule,  and  the  white  matter  external.  The  supraseg- 
mental parts  comprise  the  expanded  portions  of  the  dorsal  wall  of  the 
neural  tube  already  mentioned,  namely  the  pallium,  corpora  quad- 
rigemina,  and  cerebellum.  These  constitute  the  highest  coordi- 
nating centers  of  the  nervous  system.  Here  the  gray  matter  is  exter- 
nal, constituting  a  cortex,  and  the  white  matter  is  internal. 

The  grouping  of  peripheral  neurones  into  ganglia  and  nerves 
has  already  been  mentioned.     In  the  central  nervous  system  more  or 


THE  NERVOUS  SYSTEM 


421 


less  definite  groups  or  systems  cf  neurones  having  certain  definite  con- 
nections may  also  be  distinguished.  The  axones  of  such  a  system 
constitute  a  tract  or,  when  aggregated  into  a  definite  bundle,  a. fascicu- 
lus. The  groups  of  neurone  bodies  are  termed  nuclei.  The  group  or 
collection  of  bodies  whose  axones  form  a  certain  tract  is  the  nucleus 
of  origin  of  that  tract.  The  same  nucleus  may  receive  the  termina- 
tions of  some  other  tract  and  is  then  the  terminal  nucleus  of  that  tract. 
A  given  neurone  system  serves  as  a  path  for  the  conduction  of  some 
particular  kind  of  nerve  impulse.  A  conduction  path,  however,  is 
often  composed  of  several  neurone  systems  linked  together,  thus 
formins:  a  series  of  relavs. 


Three -rven,ron.€  a/Yer'enf su/trctseyntenlal/tei/A 

>     >   > 


jiffere/itnerinhera/ neu-    ^ 


Fig.  288. — Diagram  illustrating  an  arc  transversing  only  the  segmental,  and  an  arc 
transversing  the  suprasegmental  part  of  the  nervous  system. 


All  reactions  performed  by  the  nervous  system  must  ultimately 
take  effect  upon  some  part  of  the  body  or  effector  and  are  usually  ini- 
tiated by  changes  in  some  receptor.  Such  a  circuit  from  receptor  to 
effector  may  be  termed  a  neural  arc  (Fig.  288),  and  will  involve  affer- 
ent peripheral  neurones,  efferent  peripheral  neurones  and  usually 
intermediate  neurones.  The  complexity  of  such  arcs  depends  largely 
upon  the  number  and  character  of  intermediate  neurones  intercalated 
in  the  arc  between  the  afferent  and  efferent  peripheral  neurones. 
Such  arcs  may  obviously  traverse  centrally  only  the  cord  or  segmental 
brain  or  may  also  traverse  one  or  more  of  the  suprasegmental  parts  of 
the  nervous  system.  Intermediate  neurones  which  link  together 
different  parts  of  the  same  segment  may  be  termed  intrasegmcntal 
neurones.  Intermediate  neurones  which  link  together  different 
segments  of  the  cord  and  segmental  brain  may  be  termed  interseg- 
mental neurones.  Other  intermediate  neurones  form  conduction 
paths  to  and  from  suprasegmental  ])arts  (ajfcrciit  and  rjfrrnil  supra- 


422  THE  ORGANS 

segmental  neurones)   and  still  others  are  suprasegmental  associative 
neurones,  confined  to  suprasegmental  structures  (Fig.  288). 

MEMBRANES  OF  THE  BRAIN  AND  CORD 

The  brain  and  cord  are  enclosed  by  two  connective-tissue  mem- 
branes, the  dura  mater  and  the  pia  mater,  a  part  of  the  latter  being 
often  referred  to  as  a  separate  membrane,  the  arachnoid  (Fig,  289). 

The  dura  mater  is  the  outer  of  the  two  membranes  and  consists 
of  dense  fibrous  tissue.  The  cerebral  dura  serves  both  as  an  investing 
membrane  for  the  brain  and  as  periosteum  for  the  inner  surfaces 
of  the  cranial  bones.  It  consists  of  two  layers:  {a)  An  inner  layer 
of  closely  packed  fibro-elastic  tissue  containing  many  connective- 
tissue  cells,  and  lined  on  its  brain  surface  with  a  single  layer  of  flat 
cells ;  and  {h)  an  outer  layer,  which  forms  the  periosteum  and  is  similar 
in  structure  to  the  inner  layer,  but  much  richer  in  blood-vessels  and 
nerves.  Between  the  two  layers  are  large  venous  sinuses.  The 
spinal  dura  corresponds  to  the  inner  layer  of  the  cerebral  dura,  which 
it  resembles  in  structure,  the  vertebrae  having  their  own  separate  peri- 
osteum. The  outer  surface  of  the  spinal  dura  is  covered  with  a  single 
layer  of  flat  cells,  and  is  separated  from  the  periosteum  by  the 
epidural  space,  which  contains  anastomosing  venous  channels  lying 
in  an  areolar  tissue  rich  in  fat.  The  spinal  dura  is  said  to  contain 
lymphatics  which  open  on  both  of  its  surfaces.  Beneath  the  spinal 
dura,  between  it  and  the  arachnoid,  is  the  subdural  space,  a  narrow 
cleft  containing  a  fluid  probably  of  the  nature  of  lymph.  It  is  stated 
that  this  space  communicates  by  lymph  clefts  with  the  lymph  spaces 
in  the  sheaths  of  nerves  and  also  communicates  with  the  deep  lymph- 
atic vessels  and  glands  of  the  neck  and  groin.  It  has  no  direct  com- 
munication with  the  subarachnoid  space  (see  below). 

The  pia  mater  closely  invests  the  brain  and  cord,  extending  into 
the  sulci  and  sending  prolongations  into  the  ventricles.  It  consists 
of  fibro-elastic  tissue  arranged  in  irregular  lamellae,  forming  a  spongy 
tissue,  the  cavities  of  which  contain  more  or  less  fluid.  The  outer 
lamellas  are  the  most  compact,  and  are  covered  on  the  dural  surface 
by  a  single  layer  of  flat  cells.  It  is  this  external  layer  of  the  pia  which 
is  frequently  described  as  a  separate  membrane,  the  arachnoid. 
The  space  beneath  the  arachnoid  is  the  subarachnoid  space  and 
contains  cerebrospinal  fluid.  There  is  direct  communication  between 
these  cavities  and  the  subarachnoid  space  in  the  roof  of  the  fourth 


THE  NERVOUS  SYSTEM 


423 


ventricle.  The  subarachnoid  space  communicates  with  the  lymphatic 
spaces  within  the  nerve  sheaths.  It  is  also  stated  that  it  communi- 
cates with  the  lymph  spaces  contained  within  the  vascular  connective 
tissue  (media  and  adventitia)  of  the  blood-vessels  which  penetrate 
the  central  nervous  system.     Whether  there  is  normally    a  peri- 


vascular lymph  space  between  adventitia  and  glial  membrane  is 
doubtful  and  the  existence  has  also  been  denied,  by  good  authorities, 
of  lymph  spaces  within  the  glia,  the  glial  membrane  forming  in  normal 
conditions  a  continuous  structure.  The  inner  himclhe  of  the  i)ia  are 
more  loosely  arranged,  are  more  cellular  and  more  vascular.     Espe- 


424  -  THE  ORGANS 

daily  conspicuous  are  large,  irregular  cells  with  delicate  bodies  and 
large  distinct  nuclei.  They  lie  upon  the  connective-tissue  bundles 
partially  lining  the  spaces. 

The  Pacchionian  bodies  are  peculiar  outgrowths  from  the  outer 
layer  of  the  pia  mater  cerebralis,  which  are  most  numerous  along  the 
longitudinal  fissure.  They  are  composed  of  fibrous  tissue,  and  fre- 
quently contain  fat  cells  and  calcareous  deposits. 

Blood-vessels.- — The  spinal  dura  and  the  inner  layer  of  the  cere- 
bral dura  are  poor  in  blood-vessels.  The  outer  layer  of  the  cerebral 
dura,  forming  as  it  does  the  periosteum  of  the  cranial  bones,  is  rich 
in  blood-vessels  which  pass  into  and  supply  the  bones.  The  pia  is 
very  vascular,  especially  its  inner  layers,  from  which  vessels  pass 
into  the  brain  and  cord. 

TECHNIC 

For  the  study  of  the  structure  of  the  membranes  of  the  brain  and  spinal  cord, 
fix  pieces  of  the  cord  with  its  membranes,  and  of  the  surface  of  the  brain  with 
membranes  attached,  in  formalin-Miiller's  fluid  (technic  5,  p.  7)  and  stain  sec- 
tions with  haematoxylin-eosin  (technic  i,  p.  20). 

THE  PERIPHERAL  NERVES 

The  peripheral  nerves  are  divided  into  spinal  nerves  and  cranial 
nerves,  the  former  being  connected  with  the  cord,  the  latter  with  the 
brain.  Each  spinal  nerve  consists  of  two  parts — a  motor  or  efferent 
part  and  a  sensory  or  afferent  part.  Of  the  cranial  nerves  some  are 
purely  efferent,  others  purely  afferent,  while  still  others  consist,  like 
the  spinal  nerves,  of  both  efferent  and  afferent  fibres.  The  efferent 
fibres  of  the  spinal  nerves  are  axones  of  cell  bodies  situated  in  the 
anterior  horns  of  the  cord  (see  p.  451,  and  Figs.  308  and  318)  and 
axones  of  sympathetic  ganglion  cells.  The  former  leave  the  cord  as 
separate  bundles,  which  join  to  form  the  motor  or  efferent  root.  The 
afferent  fibres  are  peripheral  processes  of  cell  bodies  situated  in  the 
spinal  ganglia  (p.  429  and  Figs.  308,  292).  These  leave  the  ganglion 
and  join  with  the  fibres  of  the  motor  root  to  form  the  mixed  spinal 
nerve  (Fig.  308,  /) .  The  connection  of  the  ganglion  with  the  cord  is 
by  means  of  the  central  processes  of  the  spinal  ganglion  cells,  which 
enter  the  cord  as  the  posterior  root.  Among  the  afferent  fibres  of 
the  posterior  root  are  also  found,  in  some  animals,  a  few  efferent 
fibres  (Fig.  308,  c),  processes  of  cells  in  the  cord.  Some  fibres  from 
the  spinal  ganglion  and  from  the  efferent  roots  form  the  white  ramus 


THE  NERVOUS  SYSTEM 


425 


communicans  to  the  sympathetic  ganglia.  Fibres  from  the  sympa- 
thetic ganglia  form  the  gray  ramus  communicans  to  the  mixed  spinal 
nerve  (Figs.  289  and  302).  For  further  details  regarding  cranial 
nerves  see  pp.  474,  475. 

The  peripheral  nerve  consists  of  nerve  fibres  supported  by  con- 
nective tissue  (Fig.  290).  Enclosing  the  entire  nerve  is  a  sheath  of 
dense  connective  tissue,  the  epineurium.  This  sends  septa  into  the 
nerve  which  divide  the  fibres  into  a  number  of  bundles  or  fascicles. 
Surrounding  each  fascicle  the  tissue  forms  a  fairly  distinct  sheath,  the 


^e/- 


Fig.  290. — Erom  Transverse  Section  of  Human  Nerve  Trunk.  (Osmic  acid  fi.xa- 
tion.)  f  Quain.)  cp.  Nerve  sheath  or  epineurium  surrounding  the  entire  nerve  and  con- 
taining blood-vessels  (v)  and  small  groups  of  fat  cells  (/);  pri\  perifascicular  sheath  or 
perineurium  surrounding  each  bundle  or  fascicle  of  nerve  fibres;  oid,  interior  of  fascicle 
showing  supporting  connective  tissue,  the  endoneurium. 

perifascicular  sheath  or  perineurium,  which  is  covered  with  a  layer  of 
flat  cells.  From  the  perineurium,  delicate  strands  of  connective  tissue 
pass  into  the  fascicle,  separating  the  individual  nerve  fibres.  This  con- 
stitutes the  inlrafascicular  connective  tissue  or  endoneurium.  In  the 
connective-tissue  layers  of  the  perineurium  are  blood-vessels,  and 
lymph  spaces  lined  with  endothelium,  which  communicate  with 
lymph  channels  within  the  fascicle.  When  nerves  branch,  the  con- 
nective tissue  sheaths  foHow  the  branchings.  When  the  nerve 
becomes   reduced  to  a  singh-  fibre,  th(;   jx-rineural   and    endoneural 


426  THE  ORGANS 

connective  tissue  still  remaining  constitutes  the  sheath  of  Henle. 
The  space  between  the  neurilemma  and  sheath  of  Henle  has  been 
described  as  a  lymph  space  communicating  with  the  rest  of  the 
lymphatic  system  of  the  nerve.  On  emerging  from  the  central 
nervous  system,  the  root  fibres  receive  an  investment  of  connec- 
tive tissue  (endoneurium  and  perineurium)  as  they  pass  through 
the  pia  mater.  This  is  reinforced  by  additional  connective  tissue 
(epineurium,)  as  the  nerve  passes  through  the  dura  mater.  For 
description  of  medullated  and  non-medullated  nerve  fibres  see 
Chap.  VI. 

TECHNIC 

Fix  a  medium-sized  nerve,  such  as  the  human  radial  or  ulnar,  by  suspending 
it,  with  a  weight  attached  to  the  lower  end,  in  formalin- Miiller's  fluid  (technic 
5,  p.  7).  Stain  transverse  sections  in  haematoxylin-picro-acid-fuchsin  (technic 
3,  p.  21),  or  haematoxylin-eosin  (technic  i,  p.  20),  and  mount  in  balsam.  Pieces 
of  nerve  should  also  be  fixed  in  osmic  acid  imbedded,  cut,  and  mounted  without 
further  staining.  Pieces  of  fresh  nerve  may  be  tested  and  examined  without 
staining. 

THE  AFFERENT  PERIPHERAL  NEURONES 

These  comprise,  as  already  stated,  the  bodies  and  processes  of 
the  cerebro-spinal  ganglion  cells  or  cerebro-spinal  ganglionic  neurones, 
probably  some  of  the  sympathetic  ganglion  cells,  certain  cells  of  the 
retina  and  certain  cells  of  the  olfactory  mucous  membrane.  The 
two  last  named  are  described  in  connection  with  the  organs  of  special 
sense. 

The  Cerebro-spinal  Ganglia 

A  cerebro-spinal  ganglion  contains  the  bodies  of  the  cerebro-spinal 
ganglionic  neurones  whose  processes  form  the  afferent  root  of  the 
cerebro-spinal  nerve.  It  lies  in  the  dorsal  root,  a  dorsal  root  being 
that  part  of  the  nerve  which  lies  between  the  exit  of  the  dorsal  root 
fibres  from  the  cord  and  their  junction  with  the  ventral  root. 
Each  ganglion  is  surrounded  by  a  connective-tissue  capsule  which  is 
continuous  with  the  perineurium  and  epineurium  of  the  peripheral 
nerves.  (Fig.  289.)  From  this  capsule  connective-tissue  trabeculae 
extend  into  the  ganglion,  forming  a  connective-tissue  framework. 
Within  the  ganglion  the  nerve  cells  are  separated  into  irregular  groups 
by  strands  of  connective  tissue  and  by  bundles  of  nerve  fibres. 
Each  ganglion  cell  contains  a  centrally  located  nucleus  and  a  dis- 


THE  NERVOUS  SYSTEM 


427 


tinct  nucleolus,  and  is  surrounded  by  a  capsule  of  flat,  concentrically- 
arranged  cells  which  are  probably  derived  from  the  neural  plate 
(p,  418)  and  are  often  called  am pJdcytes  or  satellite  cells  (Fig.  293). 
Stained  by  Xissl's  method  the  cytoplasm  is  seen  to  contain  rather 
small,  finely  granular  chromophilic  bodies,  which  show  a  tendency 
to  concentric  arrangement  around  the  nucleus.  Pigmentation  is 
common,  the  granules  usually  forming  a  group  in  the  vicinity  of  the 
point  of  origin  of  the  main  process  of  the  cell.     The  majority  of  the 


Fig.  291. — Longitudinal  Section  through  a  Spinal  Ganglion.  X20.  (Stohr.)  a, 
Ventral  nerve  root;  b,  dorsal  nerve  root;  c,  mixed  spinal  nerve;  d,  groups  of  ganglion 
cells;  e,  nerve  fibres;/,  perineurium;  g,  fat;  h,  blood-vessel. 

cells  of  the  spinal  ganglia  have  one  principal  process  which,  at  some 
distance  from  the  cell  body,  divides  into  a  peripheral  branch  which 
becomes  an  afferent  fibre  of  the  peripheral  nerve  and  a  central 
branch  which  enters  the  cord  as  a  dorsal  root  fibre  (p.  420).  These 
cells  are  usually  called  unipolar  cells.  The  principal  process 
usually  becomes  medullated  soon  after  emerging  from  the  cell  cap- 
sule (Fig.  292). 

Among  these  cells  a  number  of  forms  have  been  distinguished  by  Dogiel: 
(a)  Cells  with  only  a  principal  process.  This  process  may  pass  almost  directly 
from  the  capsule,  but  often  takes  several  turns  around  the  cell  body,  forming  a 
"glomerulus,"  before  emerging  from  the  capsule  (Fig.  292,  i  and  Fig.  293,  .1). 
This  form  is  usually  represented  as  the  typical  cerebro-spinal  ganglion  cell,  but 
constitutes  only  a  minority  of  these  cells,  (b)  The  principal  i)rocess  gives  off 
collaterals.     These  lie  within  the  capsule  or  are  given  off  outside  the  capsule  and 


428 


THE  ORGANS 


terminate  in  other  parts  of  the  gangUon  and  its  covering,  either  in  terminal 
arborizations  or  in  terminal  enlargements  or  bulbs.  The  collaterals  may  branch. 
Some  of  the  terminations  may  be  around  the  capsules  of  other  cells.  There  may 
be  one  or  several  collaterals,  sometimes  a  number  of  very  short  intracapsular 
collaterals.  This  last  variety  of  cell  may  have  more  than  one  main  process. 
(Fig.  292,  2  and  3,  Fig.  293,  B).  (c)  Cells  with  split  processes.  Here  the  main 
process  divides  into  a  numter  of  fibres  which  reunite;  this  may  be  repeated.  The 
splitting  may  be  intracapsular  or  extracapsular.  A  variation  of  this  is  where 
there  are  two  to  six  processes  from  the  cell  which  form  a  complicated  intra- 
capsular network,  finally  uniting  to  form  the  single  main  process  (Fig.  292,  4 
and  5  and  Fig.  293,  C  and  Z)).     (d)   Cells  with  a  number  of  dendrite-like processes 


Fig.  292. — Various  Types  of  Cells  and  Nerve  Terminations  found  in  a  Spinal 
Ganglion.  Schematized  from  Dogiel.  g.r.,  gray  ramus  communicans;  sy.c,  sympa- 
thetic cell;  wj'.,  white  ramus  communicans.  a.  Spinal  ganglion;  b,  dorsal  or  afferent 
root;  c,  ventral  or  efferent  root;  d,  sympathetic  ganglion;  g,  spinal  nerve.  For  further 
explanation  see  text  (pp.  427-429).     . 

which  divide,  forming  an  intracapsular  network  which  finally  fuses  into  the  main 
process  (Fig.  292,  6).  (e)  Cells  whose  principal  process  divides  as  usual,  but 
the  peripheral  branch  terminates  by  arborizations  or  bulbs  in  the  ganglion  and 
in  its  covering,  or  in  the  neighborhood  of  the  dorsal  root  (Fig.  292,  7).  (f) 
Bipolar  cells  (Fig.  292,  8).  (g)  Multipolar  cells  with  a  number  of  intracapsular 
dendrites  and  a  main  process  (Fig.  292,  10;  Fig.  293,  E  andi^).  (h)  Cells  with 
a  principal  process  which  probably  enters,  the  dorsal  root  and  a  number  of  proc- 
esses which  may  be  dendrite-hke  in  character,  but  also  become  meduUated  in 
places,  and  which  branch  and  terminate  in  arborizations  or  bulbs  in  various 
parts  of  the  ganglion.  These  latter  apparently  collectively  represent  the  per- 
ipheral process  which  here  ends  in  the  ganglion  (Fig.  292,  9) 

The  various  endings  in  the  ganglion  of  collaterals  and  other  processes  of 
ganglion  cells  often  have  capsules  and  resemble  the  terminations  in  receptors  in 


THE  NERVOUS  SYSTEM 


429 


other  parts  of  the  body  (corpuscles  of  Pacini,  end  bulbs,  etc.)  and,  together  with 
their  envelopes,  may  represent  the  receptors  of  the  ganglion  itself  and  of  the 
connected  nerves. 

Sj-mpathetic  fibres  enter  the  ganglion  and  form  a  plexus  within  it  from  which 
fibres  pass  and  terminate  within  the  capsules  of  the  various  ganglion  cells. 


P  P 

D  E  F 

Fig.  293. — Cerebro-spinal  Ganglion  Cells  and  ihcir  Capsules.  (Cajai.)  A  (adult 
man),  Unipolar  cell  with  single  process  forming  a  glomerulus;  B  (man),  cell  with  short 
process  ending  in  intracapsular  bulb  and  main  process  giving  oil  intracapsular  collateral; 
C  Cdog),  "fenestrated"  cell  with  .several  jjroces.-^es  uniting  to  form  main  process;  D  (ass), 
more  comiilicated  form  of  the  same;  li  (man),  cell  with  short  bulbous  dendrites;  /''  (man), 
cell  with  bulbous  dendrites  and  envelo])efl  with  jjcrii  ellular  arborizations  {p.a.)  of  fdires 
(a.f.)  terminating  around  cell;  c,  collateral;  d,  di-ndrite;  p,  i)rincipal  process;  s.p.,  short 
process.     (Cajal's  silver  slain.) 

The  periphp:ral  processes  of  the  cerebro-spinal  ganglion 
CELLS  are  the  ajjereni  fibres  of  the  cerebro-spinal  nerves  (p.  424). 
The  modes  (;f  termination  of  these  i)eripherai  processes  in  receptors 


430  THE  ORGANS 

(p.  419)  are  extremely  varied  and  complicated.  These  peripheral 
terminations  are  always  free,  in  the  sense  that,  while  possibly  some- 
times penetrating  cells,  they  probably  never  become  directly  con- 
tinuous with  their  protoplasm. 

In  the  skin,  and  in  those  mucous  membranes  which  are  covered 
with  squamous  epithelium,  the  nerve  fibres  lose  their  medullary 
sheaths  in  the  subepithelial  tissue,  and,  penetrating  the  epithelial 
layer,  the  axis-cylinder  splits  up  into  minute  fibrils  (terminal  ar- 
borization) which  pass  in  between  the  cells  and  terminate  there, 
often    in    Httle    knob-like    swellings    (Fig.    294).      Such    terminal 


Fig.  294. — Free  Endings  of  Afferent  Nerve  Fibres  in  Epithelium  of  Rabbit's  Bladder. 
(Retzius.)  0,  Surfa.ce  epithelium  of  bladder;  b  g,  subepithelial  connective  tissue;  n,  nerve 
fibre  entering  epithelium  where  it  breaks  up  into  numerous  terminals  among  the  epithe- 
lial cells. 

fibrils  do  not  penetrate  among  the  squamous  cells.  Similar  "dif- 
fuse^' endings  are  found  in  serous  membranes  and  in  simple 
epithelia,  also  in  connective  tissue.  In  the  case  of  glandular  epithelia 
such  endings  may,  in  part  at  least,  be  terminations  of  efferent 
(secretory)  fibres  from  sympathetic  ganglion  cells  (p.  439).  Diffuse 
endings  have  also  been  described  on  endothelial  surfaces  such  as 
endocardium  and  in  smooth  muscle.  The  latter  are  to  be  distin- 
guished from  the  regular  motor  endings  described  below.  An  impor- 
tant form  of  diffuse  ending  is  that  found  encircling  and  ending  in 
the  outer  root  sheaths  of  hair  follicles  (Fig.  295).  Nerve  endings 
are  abundant  in  the  pulp  of  teeth.     There  has  been  some  dispute 


THE  NERVOUS  SYSTEM 


431 


as  to  whether  they  penetrate  the  dentine.  In  addition  to  such  com- 
paratively simple  nerve  endings,  there  are  also  found  in  the  skin 
and  mucous  membranes,  especially  where  sensation  is  most  acute, 
much  more  elaborate  terminations.  These  may  be  classified  as  (i) 
tactile  cells,  (2)  tactile  corpuscles,  and  (3)  end  bulbs. 


Fig.  295. — Nerves  and  Nerve  Endings  in  ihe  Skin  and  Hair  Follicles.  (After  G. 
Retzius.)  As,  Outer  root  sheath;  c,  most  sui)crficial  ncrvc-fibre  plexus  in  the  cutis: 
dr,  sebaceous  glands;  //,  the  hair  itself;  hsl,  stratum  corncum;  is,  inner  root  sheath  of 
hair;  n,  cutaneous  nerve;  rm,  stratum  gcrminativum  IMal])ighii. 

A  simple  tactile  cell  is  a  single  epithelial  cell,  the  centrally  di- 
rected end  of  which  is  in  contact  with  a  leaf-like  expansion  of  the 
nerve  terminal,  the  tactile  meniscus.  In  the  corpuscles  of  Grandry, 
found  in  the  skin  of  birds,  and  in  Merkel's  corpuscles,  which  occur 
in  mammalian  skin,  .several  epithelial  cells  are  grouped  together  to 


432 


THE  ORGANS 


receive  the  nerve  terminations.  These  are  known  as  compound  tac- 
tile cells,  the  axis  cylinder  ending  in  a  flat  tactile  disc  or  discs  between 
the  cells. 

Of  the  tactile  corpuscles  (Fig.  296)  those  of  Meissner,  which  occur 


Fig.  296.  Fig.  297. 

Fig.  296. — Tactile  Corpuscles  of  Meissner,  tactile  cell  and  free  nerve  ending.  (Mer- 
kel-Henle.)  a,  Corpuscle  proper,  outside  of  which  is  seen  in  the  connective-tissue  cap- 
sule, h,  fibre  ending  on  tactile  cell;  c,  fibre  ending  freely  among  epithelial  cells. 

Fig.  297. — Taste  Bud  from  Circumvallate  Papilla  of  Tongue.  (Merkel-Henle.)  a, 
Taste  pore;  h,  nerve  fibres  entering  taste  bud  and  ending  upon  neuro-epithelial  cells. 
On  either  side  fibres  ending  freely  among  epithelial  cells. 

in  the  skin  of  the  fingers  and  toes,  are  the  best  examples.  These 
corpuscles  lie  in  the  papilte  of  the  derma.  They  are  oval  bodies, 
surrounded  by  a  connective-tissue  capsule  and  composed  of  flattened 
cells.     From  one  to  four  medullated  nerve  fibres  are  distributed  to 


Fig.  2c 


I. — -End  Bulb  from  Conjunctiva.     (Dogiel.)     o,  Medullated  nerve  fibre,  axone 
of  which  passes  over  into  dense  end  skein. 


each  corpuscle.  As  a  fibre  approaches  a  corpuscle,  its  connective- 
tissue  sheath  becomes  continuous  with  the  fibrous  capsule,  the 
medullary  sheath  disappears,  and  the  fibrillae  of  the  terminal  abori- 
zation  pass  in  a  spiral  manner  in  and  out  among  the  epithelial  cells. 


THE  NERVOUS  SYSTEM 


433 


These  terminal  fibrils  usually  end  in  a  flattened  expansion  consisting 
of  neurofibrils  and  perifibrillar  substance.  Tactile  corpuscles  are 
also  found  on  the  volar  surface  of  the  forearm,  eyelids,  lips  and 
tip  of  the  tongue. 

Of  the  so-called  end  bulbs,  the  simplest,  which  are  found  in  the 
mucous  membrane  of  the  mouth  and  conjunctiva,  consist  of  a  central 
core  formed  by  the  usually  more  or  less 
expanded  end  of  the  usually  branched  axis 
cyHnder,  surrounded  by  a  mass  of  finely 
granular,  nucleated  protoplasm — the  inner 
bulb— the  whole  enclosed  in  a  capsule  of 
flattened  connective-tissue  cells  continuous 
with  the  sheath  of  Henle.  Other  end 
bulbs  may  be  compound.  End  bulbs  are 
found  also  in  the  mucous  membrane  of  the 
tongue,  epiglottis,  nasal  cavities,  lower 
end  of  rectum,  peritoneum,  serous  mem- 
branes, tendons,  ligaments,  connective 
tissue  of  nerve  trunks,  synovial  mem- 
branes of  certain  joints  and  external  geni- 
tals, especially  the  glans  penis  and  clitoris.^ 

The  Pacinian    bodies    (Fig.    299)    are 
laminated,  elliptical  structures  which  differ         „  t^    •  •      t.  j 

,  I'lG-    299. — racinian    Body 

from  the  more  simple  end  bulbs  already    from  Mesentery  of  Cat.    (Ran- 

j  •!     J  •    1       •      .1  i         11  vier.)     c,   Lamina   of   capsule; 

described,  mamly  m  the  greater  develop-    j,  epithelioid  cells  lying  between 

ment  of  the  perineural  capsule.      The  cap-     laminie    of    capsule;    n,   nerve 

fibre,  consistmg  of  axis  cylinder 

SUle    IS  formed   by  a  large  number  of  con-     surrounded  by  Henle's  sheath, 

entering     Pacinian     body;     /, 


perineural  sheath;  m,  mner 
bulb;  n,  terminal  fibre  which 
lireaks  uj)  at  a  into  an  irregular 
bulbous  terminal  arborization. 


As  in  the  simpler  end 


centric  lamellae,  each  lamella  consisting  of 
connective-tissue  fibres  lined  by  a  single 
layer  of  flat  connective-tissue  cells.  The 
lamcllse  are  separated  from  one  another 
by  a  clear  fluid  or  semifluid  substance, 
bulbs,  there  is  a  cylindrical  mass  of  protoplasm  within  the  cap- 
sule known  as  the  inner  bulb.  Extending  lengthwise  through 
the  centre  of  the  inner  bulb  and  often  ending  in  a  knob-like  ex- 
tremity is  the  axis  cylinder.  Arteries  in  the  vicinity  of  the  cor- 
puscle break  up  into  capillary  networks  surrounding  the  corpuscle. 

'  This  description  of  the  distril>ution  of  the  various  rc'rc,i)tors  is  principally  taken 
from  the  excellent  account  in  Sihafer's  "Text-Mook  of  Mic  roscojjic  /Nnalomy."  An 
admirable  and  still  more  tlelailcd  account  is  to  be  found  in  " 'J'lie  Nervous  System," 
by  Barker. 


434  THE  ORGANS 

From  this  network  capillaries  enter  the  corpuscle,  usually  near  the 
nerve  fibre,  and  penetrate  among  the  lamellae,  even  reaching  the 
distal  end  of  the  corpuscle.  They  do  not  enter  the  inner  bulb. 
The  Pacinian  bodies  are  found  in  the  subcutaneous  fat,  especially 
of  the  hand  and  foot,  in  the  parietal  peritoneum,  mesentery,  penis, 
clitoris,  urethra,  nipple,  mammary  gland,  in  the  vicinity  of  tendons, 
ligaments  and  joints. 

In  voluntary  muscle  afferent  nerves  terminate  in  Pacinian  cor- 
puscles, in  end  bulbs,  and  in  complicated  end  organs  called  muscle 
spindles,  or  neuromuscular  bundles.  The  muscle  spindle  (Fig.  300) 
is  an  elongated  cyhndrical  structure  within  which  are  muscle  fibres, 
connective  tissue,  blood-vessels,  and  medullated  nerves.  The 
whole  is  enclosed  in  a  connective-tissue  sheath  which  is  pierced  at 
various  points  by  nerve  fibres.  A  single  spindle  contains  several 
muscle  fibres  and  nerve  fibres.  The  muscle  fibres  differ  from  ordi-* 
nary  fibres,  being  fine  and  containing  more  nuclei  and  sarcoplasm  in 
the  middle.  The  muscle  spindles  are  more  numerous  in  the  limb 
muscles  than  in  those  of  the  trunk,  and  in  the  distal  than  the 
proximal  part  of  the  limb.  There  are  few  in  eye  muscles  and  in 
some  muscles  they  have  not  been  detected.  According  to  Ruffini, 
there  are  three  modes  of  ultimate  terminations  of  the  nerve  fibres 
within  the  spindles:  one  in  which  the  end  fibrils  form  a  series  of  rings 
which  encircle  the  individual  muscle  fibre,  termed  annular  termina- 
tions; a  second  in  which  the  nerve  fibrils  wrap  around  the  muscle 
fibres  in  a  spiral  manner — spiral  terminations ;  a  third  in  which  the 
terminations  take  the  form  of  dehcate  expansions  on  the  muscle 
fibre — arborescent  terminations . 

At  the  junction  of  muscle  and  tendon  are  found  the  elaborate 
afferent  terminal  structures,  known  as  the  muscle-tendon  organs  of 
Golgi  (Fig.  301).  This  is  a  spindle-shaped  body  composed  of  several 
tendon  bundles.  Into  this  there  enter  one  or  several  nerve  fibres 
which  break  up  into  complicated  terminal  arborizations  upon  the 
tendon  bundles. 

Other  forms  of  nerve  endings  enclosed  within  connective- tissue 
sheaths  are  corpuscles  of  Ruffini  found  in  the  subcutaneous  tissue 
of  the  finger  and  corpuscles  of  Golgi-Mazzoni  found  on  the  surfaces 
of  tendons  and  also  in  the  subcutaneous  tissue  of  the  fingers  and  in 
other  parts  of  the  skin. 

It  is  evident  from  the  above  that  the  nerve  terminations  are  only  stimulated 
through  the  intermediation  of  surrounding  cells  which  may  form  quite  elab- 


THE  NERVOUS  SYSTEM 


435 


Fig.  300. — Middle  Third  of  Muscle  Spindle  from  Striated  Voluntary  Muscle 
of  Cat.  (From  Barker,  after  RufSni.)  A,  annular  terminations;  S,  spiral  termina- 
tions; F,  arborescent  terminations. 


Fig.  301. — Tendon  of  Muscle  of  Eye  of  Ox.  (Ciarcio.)  Two  muscle-tendon  organs 
of  (iolgi,  each  showing  ring-like  and  brush-like  endings,  i^/i,  sheath  of  Henle;  sr,  node 
<i  kanvicr. 


436  THE  ORGANS 

orate  structures.  These  cells  constitute  the  receptors  and  probably  render  the 
various  nerve  terminations  they  envelop  more  or  less  inaccessible  to  all  but  one 
particular  kind  of  stimulus.  The  receptors  described  above  are  scattered  through- 
out head  and  body  {general  or  common  senses)  as  distinguished  from  those  which 
are  concentrated  into  the  organs  of  the  special  senses  (smell,  sight,  hearing,  taste) 
present  only  in  the  head  (pp.  474,  475  and  Chap.  XIII).  The  various  stimuli 
received  by  them  may  give  rise  to  sensations  of  light  pressure  or  touch  (tactile 
cells  and  tactile  corpuscles,  terminations  in  hair  sheaths),  temperature  and  pain 
(diffuse  terminations  in  epithelium  and  connective  tissue?),  muscle-tendon  sense 
of  movement  and  position  (muscle  spindles  and  possibly  end  bulbs,  etc.,  in 
muscles,  tendon  organs  of  Golgi).  These  may  be  roughly  grouped  into  general 
cutaneous  or  superficial  sensation  and  deep  sensation  (muscle-tendon  and  other 
bodily  sensations).  All  receptors,  both  of  general  and  special  senses,  may  be 
classified  (Sherrington)  as  those  receiving  stimuli  from  the  external  world  {extero- 
ceptors,  of  superficial  sensation,  smell,  sight,  and  hearing),  those  concerned 
with  visceral  reactions  {inter o-ceptors,  including  taste)  and  those  giving  infor- 
mation of  bodily  changes  {proprio-ceptors,  deep  sensation). 

The  central  processes  of  the  cerebro-spinal  ganglion 
CELLS  enter  the  central  nervous  system  as  the  fibres  of  the  afferent 
root,  the  entire  bundle  of  afferent  root  fibres  of  a  single  nerve  consist- 
ing of  all  the  central  processes  of  the  corresponding  ganglion.  Hav- 
ing entered  the  central  nervous  system,  the  central  processes  divide 
into  ascending  and  descending  arms,  as  already  mentioned  (p.  419). 
In  the  spinal  cord  the  ascending  arms  are  longer  than  the  descending 
arms.  In  the  brain  the  descending  is  usually  the  longer.  These 
arms  give  off  collaterals.  Both  collaterals  and  also  the  terminals  of 
the  arms  enter  the  gray  matter  of  the  cord  and  segmental  brain  and 
terminate  around  various  cell  bodies  and  dendrites  (terminal 
nuclei). 

THE  SYMPATHETIC  GANGLIA 

The  sympathetic  system  of  the  neck  and  trunk  consists  of  (i)  a 
series  of  vertebral  or  chain  ganglia,  lying  ventro-lateral  to  the  vertebrse, 
connected  with  the  cord  by  white  rami  communicantes  and  connected 
with  each  other  by  longitudinal  cords,  (2)  of  gangliated  prevertebral 
plexuses  connected  with  the  vertebral  ganglia  and  also  connected 
with  (3)  ill-defined  peripheral  or  terminal  ganglia  in  the  walls  of  the 
viscera  {e.g.,  plexuses  of  Auerbach  and  Meissner).  The  sympa- 
thetic ganglia  of  the  head  are  the  ciliary,  sphenopalatine,  otic,  and 
submaxillary. 

The  peripheral  processes  of  certain  spinal  ganglion  cells  pass  via 


THE  NERVOUS  SYSTEM  437 

the  white  rami  communicantes  to  the  vertebral  ganglia  and  thence  to 
visceral  receptors.  Axones  of  splanchnic  efferent  spinal  neurones 
{preganglionic  fibres)  pass  from  the  spinal  cord  via  the  ventral  roots 
and  white  rami  communicantes  to  terminate  in  various  sympathetic 
ganglia.  The  axones  of  the  cells  of  these  ganglia  {postganglionic 
fibres)  complete  the  path  by  passing  to  the  splanchnic  effectors  (heart 
muscle,  smooth  muscle  or  gland).  Thus  while  the  somatic  efferent 
peripheral  path  consists  of  only  one  neurone,  whose  body  is  in  the 
ventral  gray  of  the  cord  or  brain,  and  whose  axone  passes  without 
interruption  to  the  striated  voluntary  muscle,  the  splanchnic  efferent 
peripheral  path  (except  the  branchiomotor)  consists  of  two  neurones. 
The  first  neurone  body  is  in  the  gray  of  the  cord  or  brain,  the  second 
neurone  body  is  in  a  sympathetic  ganglion.  The  preganglionic 
fibres  emerging  in  the  seventh  cervical  to  the  third  lumbar  spinal 
roots  end  either  in  the  vertebral  or  prevertebral  (coeliac,  superior 
mesenteric,  inferior  mesenteric)  ganglia.  The  vertebral  ganglia  send 
part  of  their  axones  to  the  peripheral  nerves  {gray  rami  communicantes), 
thence  passing  to  superficial  splanchnic  effectors  (smooth  muscle  of 
hairs  and  of  superficial  blood-vessels  and  glands  of  skin).  Other 
axones  may  pass  to  the  head.  The  axones  of  the  prevertebral 
ganglia  pass  to  the  glands  and  smooth  muscle  of  the  viscera  (Fig. 
302).  The  other  segments  of  the  cord  do  not  send  out  white  rami 
communicantes  except  the  second,  third  and  fourth  sacral.  These 
fibres  do  not  communicate  with  vertebral  ganglia  but  terminate  in 
prevertebral  (pelvic)  ganglia,  which  in  turn  send  axones  to  the  lower 
colon,  rectum,  bladder  and  genitals.  In  the  head,  preganglionic 
fibres  emerge  with  the  third  nerve  and  pass  to  the  ciliary  ganglion, 
thence  as  postganglionic  fibres  to  the  ciliary  and  sphincter  iridis 
muscles  of  the  eye;  others  emerge  with  the  seventh  and  pass  to  the 
sphenopalatine  and  submaxillary  ganglia;  others  with  the  ninth  and 
pass  to  the  otic  ganglion.  Many  of  the  axones  of  these  ganglia  pass 
to  the  salivary  gland,  others  may  be  vasomotor.  The  vagus  nerve 
sends  preganglionic  fibres  to  most  of  the  viscera.  These  fibres  prob- 
ably terminate  in  the  peripheral  sympathetic  ganglia.  There  is 
thus  a  cranial  (III,  VII,  IX  and  X  nerves),  thoraco-lumbar  and  sacral 
outflow  of  preganglionic  fibres.  Most  visceral  structures  appear  to 
receive  a  double  innervation,  one  from  the  thoraco-lumbar  and  one 
from  either  the  cranial  or  sacral  system.  By  some  writers  the  term 
sympathetic  has  been  restricted  to  the  thoraco-lumbar,  the  two  others 
being  termed  autonomic. 


438 


THE  ORGANS 


Smooth  muscle    Type  II? 


Somatic  efferent 

Somatic  afferent 

Splanchnic  cerebrospinal  afferent 

Splanchnic  cerebrospinal  efferent 

Sympathetic 


White  r.  com.  .i- — - 
Gray  r.  com.  -- 


Vertebral  or 
chain  gang. 


•Sens,  ending 

Pacinian 
corpuscle 

Fig.  302.— Diagram  of  the  Sympathetic  System  and  the  Arrangement  of  its  Neu- 
rones m  a  Mammal.  On  the  left  are  shown  the  typical  elements  of  a  trunk  segment 
mcludmg  the  sympathetic  system.  On  the  right  are  shown  only  the  somatic  afferent 
and  efferent  neurones  of  the  spinal  nerve.  Of  the  sympathetic  system  are  shown  the 
white  and  gray  rami,  three  gangha  of  the  chain,  one  prevertebral  ganghon  and  one 
peripheral  ganglion.  The  symbols  used  are  explained  in  the  figure.  In  most  respects 
the  diagram  follows  one  of  Huber's  figures.     (Johnston.) 

It  will  be  noted  that  the  sympathetic  outflow  from  any  particular  cord  segment  may 
ultimately  reach  other  segments  of  the  body. 


THE  NERVOUS  SYSTEM 


439 


Some  of  the  sympathetic  cells  are  probably  afferent  but  the  ma- 
jority are  eft'erent.  The  fibres  of  the  white  rami  communicantes  are 
mostly  fine  and  medullated.  The  axones  of  the  sympathetic  cells  are 
line  and  non-medullated  or  thinly  medullated.  For  further  details 
see  Fig.  302. 

The  larger  ganglia  resemble  the  spinal  ganglia  in  having  a  connec- 
tive-tissue capsule  and  framework.  The  cells  are  smaller  and  often 
densely  pigmented.     Each  cell  is  surrounded  by  a  capsule  of  cells 


Fig.  303. — Sympathetic  Nerve  Cells  (woman  of  36  years).  (Cajal.)  A  and  B, 
cells  whose  dendrites  (h)  form  a  pericellular  plexus.  C,  cell  with  long  dendrites,  a, 
axone;  c  and  d,  terminal  part  of  a  dendrite.  The  capsular  cells  are  faintly  indicated. 
(Cajal's  silver  stain.) 


similar  to  those  surrounding  the  spinal  ganglion  cells.  Often  two  or 
three  cells  and  their  interlocked  dendrites  are  enclosed  within  a  com- 
mon capsule  (Fig.  304,  A). 

The  typical  sympathetic  nerve  cell  is  a  multipolar  cell  with  short 
branching  dendrites  confined  to  the  capsule  of  the  cell  and  often  inter- 
locked with  the  dendrites  of  adjacent  cells,  forming  glomeruli. 
Sometimes  a  dendrite  will  pass  some  distance  from  the  cell,  arborize, 
and  interlock  with  a  similar  dendritic  arborization  of  another  cell. 
Another  form  of  sympathetic  cell  has  long  slender  dendrites  often 
indistinguishable  from  axones.     These  cells  are  more  frequent  in  the 


440 


THE  ORGANS 


peripheral  ganglia.     Some  of  these  cells  have  been  considered  to  be 
afferent  sympathetic  cells.     (Figs.  303  and  304.) 


a.f.   a.f. 

Fig.  304. — Sympathetic  Nerve-cells  and  their  Capsules.  (Cajal.)  A,  Two-celled 
glomerulus;  B,  cell  surrounded  with  the  pericellular  terminal  arborizations  of  two  fibres 
(a.f.)  passing  to  the  cell;  a,  axones;  d,  fibre,  probably  dendritic,  with  bulbous  termina- 
tion.    (Cajal's  silver  stain.) 

The  sympathetic  cells  receive  fibres  which  form   arborizations 
around  and  within  their  capsules  and  also  around  the  long  dendrites. 
Many  of  these  are  terminations  of  the  visceral 
cerebro-spinal  efferent  neurones,  ie.,   the  pre- 
ganglionic fibers  (Figs   302  and  304,  B). 

As  already  noted,  the  axones  of  the  efferent 
sympathetic  cells  terminate  in  heart  muscle 
(cardio-motor),  in  smooth  muscle  of  viscera 
(viscero-motor),  of  blood-vessels  (vaso-motor) 
and  of  hairs  (pilomotor),  and  in  glandular 
epitheHa  (secretory).  In  heart  muscle  (Fig. 
ings'''on°H^art''Mus'de  ^©5)  and  in  smooth  muscle  (Fig.  306)  the 
S^^^^-  Tx''"f^°"^   Barker,    nerves  of  the  sympathetic  system  end  in  fine 

after     Ruber     and     De      .  .  .         r    ri  .  ■  .  •  •,      •  -.i 

Witt.)  jeitworks  oj  jiores,  which  are  m  relation  with 


THE  NERVOUS  SYSTEM  441 

the  muscle  cells.  Satisfactory  differentiation  between  efferent 
terminals  and  afferent  terminals  in  heart  and  in  smooth  muscle  has 
not  yet  been  made. 

In  organs  whose  parenchyma  is  made  up  of  glandular  epithelium, 
the  sympathetic  nerves  terminate  mainly  in  free  endings  which  lie 
in  the  cement  substance  between  the  cells,  thus  coming  in  contact 
with,  though  not  penetrating,  the  epithelial  cells. 


Fig.  306. — Xerve  Endings  on  Smooth  IMuscle  Cells.     (From  Barker,  after  Huber  and 
De  Witt.)     a,  .\xis  cylinder;  h,  its  termination;  n,  nucleus  of  muscle  cell. 

TECHNIC 

(i)  Fix  spinal  and  sympathetic  ganglia  in  formalin-Mtiller's  fluid  (technic  5, 
p.  7).  Stain  sections  with  haematoxylin-eosin  (technic  i,  p.  20),  or  with  haema- 
toxylin-picro-acid-fuchsin  (technic  3,  p.  21). 

(2)  Fix  spinal  and  sympathetic  ganglia  in  absolute  alcohol  or  in  lo-per-cent. 
formalin,  and  stain  sections  by  Nissl's  method  (technic,  p.  38). 

(3)  See  also  technic  i,  p.  446. 

(4)  Ganglia  should  also  be  prepared  by  Cajal's  silver  method,  using  the  al- 
cohol fixation  (p.  37). 

EFFERENT  PERIPHERAL  CEREBRO -SPINAL  NEURONES 

It  has  been  seen  that  the  bodies  of  these  neurones  lie  in  the  ventral 
part  of  the  neural  tube  where  they  form  a  part  of  the  ventral  gray 
column  in  the  cord  and  the  "motor"  nuclei  of  cranial  nerves  in  the 
segmental  brain.  The  axones  of  these  cell  bodies  emerge  as  the 
eflerent  roots  and  usually  either  pass  {via  the  white  ramus  com- 
municans,  in  spinal  nerves)  to  various  sympathetic  ganglia  to  ter- 
minate there,  or  proceed  as  the  efferent  fibres  of  the  peripheral  nerves 
to  terminate  in  the  striated  voluntary  muscles  of  the  body  and  head. 
In  the  sj)inal  nerves  these  fibres  pass  beyond  the  spinal  ganglia  and 
then  join  the  afferent  fibres;  in  some  cranial  nerves  they  pass  out 
with  the  afferent  fibres.  Ontheir  way  to  the  muscles  the  motor  axones 
may  bifurcate  several  times,  thus  allowing  one  neurone  to  innervate 


442 


THE  ORGANS 


more  than  one  muscle  fibre.  In  the  perimysium  the  nerve  fibres 
undergo  further  branching,  after  which  the  fibres  lose  their  medul- 
lary sheaths  and  pass  to  the  individual  muscle  fibres.  Here  each 
fibre  breaks  up  into  several  club-like  terminals.  These  terminals 
are  imbedded  in  a  nucleated  protoplasmic  mass  on  the  outside  of 
the  muscle  fibre  and  probably  composed  of  sarcoplasm.  It  is  stated 
that  the  neurilemma  of  the  nerve  fibre  is  continous  with  the  sarco- 
lemma  and  that  a  continuation  of  the  sheath  of  Henle  covers  the 


fV-; 


Fig.  307. — Motor  nerve-endings  in  abdominal  muscles  of  a  rat.     Gold  preparation. 

X170.     (Szymonowicz.) 

whole  structure  which  is  known  as  the  motor  end  plate.  As  a  rule 
each  muscle  fibre  is  supplied  with  a  single  end  plate,  though  in  large 
fibres  there  may  be  several.     (Fig.  307.) 

THE  SPINAL  CORD 

The  spinal  cord  encased  in  its  membranes  lies  loosely  in  the  ver- 
tebral canal,  extending  from  the  upper  border  of  the  first  cervical 
vertebra  to  the  middle  or  lower  border  of  the  first  lumbar  vertebra. 
It  is  cylindrical  in  shape  and  continuous  above  with  the  medulla 
oblongata,  while  below  it  terminates  in  a  slender  cord,  the  filum  ter- 
minate. At  two  levels,  one  in  its  cervical  and  one  in  its  lumbar 
region,  the  diameter  of  the  cord  is  considerably  increased.  These  are 
known,  respectively,  as  the  cervical  and  lumbar  enlargements.  The 
spinal  nerve  roots  leave  the  cord  at  regular  intervals,  thus  indicating 


THE  NERVOUS  SYSTEM 


443 


a  division  of  the  cord  into  segments,  each  segment  extending  above 
and  below  its  nerve  roots  one-half  the  distance  to  the  next  adjacent 
roots.  There  are  31  segments  corresponding  to  the  31  spinal  nerves; 
8  cervical,  12  thoracic,  5  lumbar,  5  sacral,  and  i  coccygeal. 


Origin  of  the  Fibres  which  Make  up  the  White  Matter  of  the  Cord 

It  has  already  been  observed  that  the  white  matter  of  the  cord  is 
composed  mainly  of  medullated  nerve  fibres,  most  of  which  run  in  a 
longitudinal  direction.  From  the  study  of  the  neurone  it  follows  that 
each  of  these  fibres  must  be  the  axone  of  some  nerve  cell.  The 
bodies  of  these  cells,  the  medullated  axones  of  which  form  the  white 
matter  of  the  cord  are  situated  as  follows: 


Cells  outside  the  spinal 
cord.  {Extrinsic  cells.) 


Cells  situated  in  the  gray 
matter  of  the  cord.  {In- 
trinsic cells.) 


(i)  Cells  outside  the  central  nervous  system 
(spinal  ganglion  cells). 

(2)  Cells  in  other  parts  of  the  central  nervous 
system  (the  brain). 

(3)  Root  cells,  such  as  those  of  the  anterior 
horn,  whose  axones  form  the  ventral  root 
(efferent  peripheral  neurones).  These  pass 
out  directly,  and  thus  do  not  become  longi- 
tudinal column  fibres. 

(4)  Intermediate  neurones,  whose  axones  enter 
into  formation  of  the  fibre  columns  of  the 
cord  (column  cells.) 

(5)  Cells  of  Golgi,  type  II,  the  axones  of  which 
ramify  in  the  gray  matter.  (These  cells  do 
not  give  rise  to  fibres  of  the  white  matter, 
but  are  conveniently  mentioned  here  among 
the  other  cord  cells.) 

(i)  The  Spinal  Ganglion  Cell  and  the  Origin  of  the 
Posterior  Columns 

It  has  already  been  seen  that  the  central  processes  of  these  cells 
enter  the  cord  as  dorsal  root  fibres  and  split  into  ascending  and  de- 
scending longitudinal  arms  composing  the  greater  part  of  the  dorsal 
funiculus  and  the  zone  of  Lissauer.  They  are  described  more  in 
detail  later  (pp.  46:  and  462). 

(2)  Cells  Situated  in  Other  Parts  of  the  Central  Nervous 
System  which  Contribute  Axones  to  the  White  Columns 
OF  THE  Cord. 
These  cells  are  situated  in  the  motor  areas  of  the  cortex  of  the 


444 


THE  ORGANS 


pallium,  in  the  midbrain,  cerebellum(?),  and  various  parts  of  the 
segmental  brain.  The  axones  of  these  cells  pass  down  the  cord, 
forming  the  descending  fibre  tracts  of  the  cord  (p.  464).  Collaterals 
and  terminals  of  these  fibres  enter  the  gray  matter  of  the  cord  to  ter- 
minate there. 


Fig.  308. — Transverse  Section  through  Spinal  Cord  and  Posterior  Root  Ganglia  of 
an  Embryo  Chick.  (Van  Gehuchten.)  a,  Spinal  ganglion,  its  bipolar  cells  sending  their 
peripheral  processes  outward  to  become  fibres  of  the  mixed  spinal  nerve  (/),  their  central 
processes  into  the  dorsal  columns  of  the  cord  as  the  dorsal  root  fibres  ih) ;  within  the  pos- 
terior columns  these  fibres  can  be  seen  bifurcating  and  sending  collaterals  into  the  gray 
matter  of  the  posterior  columns,  one  collateral  passing  to  the  gray  matter  of  the  opposite 
side.  The  few  efferent  fibres  of  the  dorsal  root  (c)  are  disproportionately  conspicuous. 
The  large  multipolar  cells  of  the  ventral  horns  are  seen  sending  their  axones  {d)  out  of  the 
cord  as  the  ventral  root  fibres  (e)  which  join  the  peripheral  processes  of  the  spinal  gang- 
lion cells  to  form  the  mixed  spinal  nerve  (/) ;  col,  collateral  from  axone  of  ventral  horn  cell. 
Dendrites  of  the  anterior  horn  cells  are  seen  crossing  the  median  line  in  the  anterior  com- 
missure. About  the  centre  of  the  cord  is  seen  the  central  canal;  dorsal  and  ventral  to 
the  latter  some  ependymal  cells  stretching  from  the  canal  to  the  periphery  of  the  cord. 
(Golgi  Method.) 

(3)  Root  Cells — Motor  Cells  oe  the  Anterior  Horn 

The  course  of  the  axones  of  these  cells  has  been  described  (p.  441). 
The  bodies  are  described  on  pp.  451  and  452. 

(4)  Column  Cells 

These  are  cells  which  lie  in  the  gray  matter  of  the  cord  and  send 
their  axones  into  the  white  columns  or  funiculi  (see  p.  450)  where 
they  either  bifurcate  or  turn  up  or  down,  becoming  longitudinal 
fibres.  Some  of  the  cells  send  their  axones  into  the  white  matter  of 
the  same  side  of  the  cord.  These  are  known  as  tautomeric  cells 
(Fig.  309,  3).  Others  send  their  axones  as  fibres  of  the  anterior 
commissure  to  the  white  matter  of  the  opposite  side  of  the  cord — 


THE  NERVOUS  SYSTEM 


445 


heteromeric  cells  (Fig.  309,  i  and  2).  The  axones  of  a  few  cross  in  the 
dorsal  white  commissure.  In  a  few  others  the  axone  divides,  one 
branch  going  to  the  white  matter  of  the  same  side,  the  other  to  the 
white  matter  of  the  opposite  side — hecateromeric  cells  (Fig.  309,  4). 

The  axones  of  many  of  these  cells  are  short,  constituting  the  short 
fibre  tracts  (fundamental  columns — ground  bundles)  of  the  cord  (see 


Fig.  309. — Transverse  Section  through  Spinal  Cord  of  Embryo  Chick  of  Seven 
Days  Incubation  (Golgi  Preparation).  The  boundary  between  the  future  gray  and 
white  matter  is  indicated  by  the  doited  line,  i  and  2,  Heteromeric  column  cells  whose 
axones  (ax)  pass  through  the  anterior  commissure  to  the  opposite  ventral  white  columns; 
3,  tautomeric  column  cells  whose  axone  (ax)  ])asses  to  the  ventro-lateral  white  column 
on  the  same  side;  4,  hecateromeric  column  cell  whose  axone  (ax)  bifurcates,  one  branch 
entering  the  ventral  white  column  of  the  same  side  and  the  other  branch  i)assing 
through  the  anterior  commissure  to  the  opposite  side.  A  number  of  longitudinal 
fibres  in  the  white  columns  are  shown,  cut  transversely  or  obliqucl3\ 

page  468 ;  others  form  lon^  ascending  fibre  tracts,  jmssing  up  through 
the  cord  to  the  brain  (see  page  461.  Terminals  and  collateral 
branches  of  these  longitudinal  axones,  especially  of  the  short  ones, 
are  constantly  re-entering  the  gray  matter  to  end  in  arbori/alions 
around  the  nerve  cells  (Fig.  310). 


446 


THE  ORGANS 


(5)  Cells  or  Golgi  Type  II 

The  axones   of  these  cells  do  not  leave  the  gray  matter,  but 

divide  rapidly  and  terminate  in  the 
gray  matter  near  their  cells  of  origin, 
some  crossing  to  terminate  in  the 
gray  matter  of  the  opposite  side. 

TECHNIC 

(i)  For  the  purpose  of  studying  the 
spinal  ganglion  cell  with  its  processes  and 
their  relations  to  the  peripheral  nerves  and 
to  the  cord,  the  most  satisfactory  material 
is  the  embryo  chick  of  six  days'  incubation, 
treated  by  the  rapid  silver  method  of  Golgi 
(technic  b,  p.  35).  Rather  thick  (75/^) 
transverse  and  longitudinal  sections  are 
made  and  mounted  in  balsam  without  a 
cover-glass.  Owing  to  the  uncertainty  of 
the  Golgi  reaction,  several  attempts  are 
frequently  necessary  before  good  sections 
are  obtained. 

(2)  The  root  cells  of  the  anterior  horn 
with  their  axones  passing  out  of  the  cord 
and  joining  the  peripheral  processes  of  the 
spinal  ganglion  cells  to  form  the  spinal 
nerves,  can  usually  be  seen  in  the  trans- 
verse sections  of  the  six-day  embryo  chick 
cord  prepared  as  above,  technic  (i). 

(3)  For  studying  the  column  cells  of 
the  cord,  embryo  chicks  of  from  five  to  six 
days'  incubation  should  be  treated  as  in 
technic  (i).  Owing  to  the  already  men- 
tioned uncertainty  of  the  Golgi  reaction,  it 
is  usually  necessary  to  make  a  large  num- 
ber of  sections,  mounting  only  those  which 
are  satisfactorily  impregnated.  It  is  rare 
for  a  'single  section  to  show  all  types  of 
cells.  Some  sections  contain  tautomeric 
cells,  some  contain  heteromeric,  some  both, 
while  in  very  few  will  the  hecateromeric 
type  be  found. 

Sections  containing  fewest  impregnated 
cells    frequently    show  collaterals   to   best 
fringe  of  fine  transverse  fibres  crossing  the 
and  white  matter. 


Fig.  310. — From  Longitudinal 
Section  of  Spinal  Cord  of  Embryo 
Chick.  (Cajal.)  A,  White  column 
of  cord;  B,  gray  matter.  The  cells 
of  the  gray  matter  (column  cells)  are 
seen  sending  their  axones  into  the 
white  matter,  where  they  bifurcate, 
their  ascending  and  descending  arms 
becoming  fibres  of  the  white  column. 
The  dendrites  of  these  cells  are  seen 
ramifying  in  the  gray  matter.  To 
the  left  are  seen  fibres  (posterior  root 
fibres)  entering  the  white  matter  and 
bifurcating,  the  ascending  and  de- 
scending arms  becoming  fibres  of  the 
white  column.  From  the  latter  are 
seen  fibres  (collaterals  and  terminals) 
passing  into  the  gray  matter  and  end- 
ing in  arborizations  (Golgi  Method). 

advantage.     These  are  seen  as  a 
boundary  line  between  gray  matter 


THE  NERVOUS  SYSTEM  447 

(4)  The  silver  method  of  Cajal,  using  the  alcohol  fixation  (technic  2,  p.  38), 
may  also  be  advantageously  used  to  display  many  of  the  above  details  of  struc- 
ture in  embryo  chicks.     It  is  also  capricious. 

Whole  neurones  with  long  axones  obviously  cannot  be  directly  demonstrated 
in  single  sections.  To  demonstrate  these  serial  sections  and  indirect  methods 
(degeneration,  etc.)  are  used  (see  Fibre  Tracts  of  Cord). 

PRACTICAL  STUDY 

Transverse  Section  of  Six-day  Chick  Embryo  (Technic  i,  p.  446). — Using 
a  lower-power  objective,  first  locate  the  cord  and  determine  the  outlines  of  gray 
matter  and  white  matter.  Observe  the  spinal  ganglia  lying  one  on  either  side 
of  the  cord  (Fig.  308,  a).  At  least  one  of  the  ganglia  will  probably  show  one  or 
more  bipolar  cells,  sending  one  process  toward  the  periphery,  the  other  toward 
the  spinal  cord.  Note  that  the  peripheral  process  is  joined,  beyond  the  ganglion, 
by  fibres  which  come  from  the  ventral  region  of  the  cord  (fibres  of  the  anterior 
root).  In  some  specimens  the  latter  can  be  traced  to  their  origin  in  the  cells 
of  the  anterior  horn  (Fig.  308,  d).  The  union  of  the  peripheral  processes  of  the 
spinal  ganglion  cells  and  the  anterior  horn  fibres  is  seen  to  make  up  the  mixed 
spinal  nerve  (Fig.  308,  /).  Observe  the  central  processes  of  the  spinal  ganglion 
cells  entering  the  dorsal  column  of  the  cord  and  bifurcating  (Fig.  308,  b).  As 
these  branches  pass  up  and  down  the  cord,  only  a  short  portion  of  each  can  be 
seen  in  a  transverse  section.  Note  the  fibres  (collaterals)  passing  from  the  white 
matter  into  the  gray  matter.  The  fact  that  they  are  finer  than  the  longitudi- 
nal fibres  in  the  white  matter  shows  that  they  are  branches  of  the  latter. 
Even  in  transverse  section  the  point  at  which  they  leave  the  latter  may  occa- 
sionally be  made  out.  Note  in  some  of  the  sections  a  little  round  mass  just 
ventral  and  to  the  inner  side  of  the  spinal  ganglion,  in  which  nerve  cells  may 
be  seen,  and  some  fibres  passing  into  or  out  of  it.  This  represents  the  begin- 
ning of  the  sympathetic  system  with  its  chain  of  ganglia.  Note  the  relation 
which  this  bears  to  the  spinal  cord  and  spinal  ganglia. 

In  the  same  or  other  transverse  sections  study  the  column  cells  of  the  cord, 
carefully  distinguishing  between  the  dendrites  and  axone.  This  is  not  always 
easy,  but  the  axone  can  usually  be  distinguished  as  being  more  slender,  with 
smoother  outline  and  more  uniform  size  throughout  its  course.  Axones  may 
come  off  from  dendrites  as  well  as  from  the  cell  bodies.  At  least  one  tautomeric 
and  one  heteromeric  column  cell  shouhl  be  found  and  studied  (Fig.  309).  Study 
also  the  collaterals  if  they  are  stained.  Remember  that  only  a  few  of  the  elements 
present  are  stained  in  Golgi  preparations  and  that  there  are  apt  to  be  present 
irregular  silver  precipitates  without  any  significance.  Capillaries  often  appear 
as  a  coarse  brown-stained  meshwork. 

Study  also  any  spongioblasts  that  may  be  stained.  Tho.se  with  nuclei  near 
the  central  canal  give  a  fair  representation  of  the  ependyma  cells  of  the  adult 
cord,  except  the  cell  does  not  usually  in  (he  latter  extend  entirely  through  the 
wall  of  the  neural  tube. 

Longitudinal  Section  of  Six-day  Chick  Embryo  Ciec  hnic  i,  p.  446).  -  Using 
a  low-power  objective  locale  gray  matter  and  white  matter  and  identify  i)lane 


448  THE  ORGANS 

of  section  relative  to  transverse  section  above  described.  Note  in  the  white 
matter  longitudinally-running  fibres  from  which  branches  pass  off  into  the  gray 
matter  (Fig.  310).  The  longitudinal  fibres  of  the  posterior  columns  are  the  as- 
cending and  descending  branches  of  the  central  processes  of  the  spinal  ganglion 
cells,  and  the  branches  passing  into  the  gray  matter  are  their  collaterals  and 
terminals.  If  the  section  happens  to  include  the  entering  fibres  of  a  posterior 
root,  these  can  be  seen  branching  in  the  posterior  columns  into  ascending  and 
descending  arms  (Fig.  310).  The  longitudinal  fibres  of  the  lateral  and  anterior 
columns  are  axones  of  column  cells  and  of  cells  situated  in  higher  centres  (see 
pages  444  and  445).  These  also  send  collaterals  and  terminals  into  the  gray 
matter. 

General  Topography  of  the  Cord,  Cell  Groupings,  Arrangement  of 
Fibres  and  Finer  Structure 

The  further  description  of  the  cord  is  best  combined  with  the 
practical  study  of  sections  of  the  cord,  taking  sections  through  the 
lumbar  enlargement  as  a  type. 

PRACTICAL  STUDY  OF  SECTIONS  THROUGH  LUMBAR 
ENLARGEMENT 

General  Topography  (Figs.  311  and  312). — The  general  features  of  the  sec- 
tions can  be  best  seen  with  the  naked  eye  or  with  a  low-power  dissecting  lens. 

Note  the  shape  and  size  of  the  cord,  and  that  it  is  surrounded  by  a  thin  mem- 
brane, the  pia  mater  spinalis;  the  deep  anterior  median  fissure,  into  which  the 
pia  mater  extends;  the  posterior  median  septum  consisting  principally  of  neuroglia, 
over  which  the  pia  mater  passes  without  entering;  and  the  postero-lateral  grooves 
or  sulci  at  the  entrance  of  the  posterior  root  fibres.  The  gray  matter  is  seen  in 
the  central  part  of  the  section  (stained  more  lightly  in  the  Weigert  preparation, 
on  account  of  the  presence  of  numerous  unstained  cell  bodies  and  dendrites)  and 
arranged  somewhat  in  the  form  of  the  letter  H.  Dorsally  the  gray  matter  extends 
almost  to  the  surface  of  the  cord  as  the  dorsal  gray  columns  {posterior  horns  or 
cornua).  The  ventral  gray  columns  {anterior  horns)  are,  on  the  other  hand, 
short  and  broad,  and  do  not  approach  the  surface  of  the  cord.  Surrounding  the 
gray  matter  is  the  white  matter  (stained  deep  blue  in  the  Weigert  preparation). 
This  is  divided  by  the  posterior  horn  into  two  parts,  one  lying  between  the  horn 
and  the  posterior  median  septum,  the  posterior  funiculus  {dorsal  white  column) ; 
the  other  comprising  the  remainder  of  the  white  matter,  the  antero-lateral funicu- 
lus {antero-lateral  white  column).  This  latter  is  again  divided  by  the  anterior 
horn  and  anterior  nerve  roots  into  a  lateral  funiculus  {lateral  white  column)  and 
an  anterior  funiculus  {ventral  white  column).  In  the  concavity  between  the  an- 
terior and  posterior  horns  some  processes  of  the  gray  matter  extend  out  into  the 
white  matter  where  they  interlace  with  the  longitudinally  running-fibres  of  the 
latter  to  form  the  reticular  process  (not  well  marked  in  the  lumbar  cord). 

For  the  study  of  further  details  the  low-power  objective  should  be  used. 


THE  NERVOUS  SYSTEM 


449 


Gray  :Matter.— In  the  cross  portion  of  the  H  is  seen  the  central  canal, 
usually  obliterated  in  the  adult  and  represented  only  by  a  group  of  epithelial 
cells.  The  central  canal  divides  the  gray  matter  connecting  the  two  sides  of  the 
cord  into  a  ventral  gray  commissure  and  a  dorsal  gray  commissure.  Immediately 
surrounding  the  epithelial  cells  is  a  light  granular  area  composed  mainly  of 
neuroglia  and  known  as  the  central  gelatinous  substance.     Toward  the  surface  of  the 


rt  C  rt  B 


•..        •,       V^  2  P  S  Q-;3 
"  o  ":  rt  O  °:      rt  J;  g 


<u  JiJ 
2   <-> 

H 

^  a 


cord  the  posterior  horn  expands  into  a  head  or  ca/>M/,  external  to  which  is  an  area 
similar  in  general  appearance  to  that  surrounding  the  central  canal,  the  gelatinous 
substance  of  Rolando.  The  head  is  connected  with  the  base  of  the  dorsal  horn 
by  a  narrower  neck  or  cervix.  External  to  the  gelatinous  substance  of  Rolando 
is  a  thin  zone  containing  a  plexus  of  fine  medullatcd  fibres  (Weigert  stain)  known 
as  the  marginal  zone  or  zona  spongiosa,  and  external  to  this,  occupying  the  space 
20 


450  THE  ORGANS 

between  it  and  the  periphery,  is  a  zone  composed  of  fine  longitudinal  meduUated 
fibres  rather  sparsely  arranged  and  therefore  staining  more  lightly  with  the  Wei- 
gert  method.  This  is  the  zona  teryninalis  or  zone  of  Lissauer.  It  belongs  ob- 
viously to  the  white  matter  of  the  cord  (see  page  452).  The  portion  of  the  gray 
matter  connecting  the  dorsal  and  ventral  horns  may  be  termed  the  intermediate 
or  middle  gray.  Note  the  well-defined  groups  of  large  nerve  cells  in  the  anterior 
horns  and  the  fibres  passing  out  from  the  anterior  horns  to  the  surface  of  the  cord, 
ventral  {anterior)  nerve  roots.     (Figs.  311  and  312.) 

White  Matter. — Note  the  general  appearance  of  the  white  matter  and  the 
disposition  of  the  supporting  strands  of  neuroglia  tissue  (light  in  the  Weigert, 
usually  darker  in  other  stains).  The  neuroglia  is  seen  to  form  a  fairly  thick 
layer  just  beneath  the  pia  mater  from  which  trabeculae  pass  in  among  the  fibres, 
the  broadest  strand  forming  the  posterior  median  septum.  If  the  section  has 
been  cut  through  a  dorsal  {posterior)  nerve  root,  a  strong  bundle  of  dorsal  root 
fibres  can  be  seen  entering  the  white  matter  of  the  cord  along  the  dorsal  and  mesial 
side  of  the  posterior  horn.  Just  ventral  to  the  anterior  gray  commissure  is  a 
bundle  of  transversely-running  meduUated  fibres — the,  anterior  white  commissure. 
(Fig.  312.)  It  is  composed  of  the  axones  of  various  heteromeric  column  cells, 
and  of  decussating  terminals  of  various  fibres.  In  the  dorsal  part  of  the  dorsal 
gray  commissure  are  also  a  few  fine  transversely  running  meduUated  nerve 
fibres — the  dorsal  white  commissure.  It  consists  of  collaterals  of  fibres  in  dorsal 
funiculi  and  axones  of  heteromeric  column  cells. 

Cell  Groupings. — The  positions  and  groupings  of  the  various  cell  bodies 
should  now  be  studied.  (Nissl,  Hsematoxylin-Eosin,  Cajal,  Figs.  311  and  312.) 
(For  convenience,  their  general  arrangement  throughout  the  cord  is  here 
given;  also  the  course  of  their  axones,  though  this  is  usually  only  seen  in  Golgi 
preparations.) 

(A)  Cells  of  the  Dorsal  Horn. — (a)  Marginal  cells  arranged  tangentially 
to  the  border  of  the  gelatinous  substance  of  Rolando,  (b)  Cells  in  the  gelatinous 
substance  of  Rolando,  arranged  radially.  The  Golgi  method  indicates  that  the 
axones  of  (a)  and  (b)  principally  enter  the  adjoining  lateral  column,  (c)  Large 
stellate  cells  in  the  apex  of  the  caput,  most  of  the  axones  of  which  go  to  the  lateral 
columns,  but  some  cross  in  the  ventral  white  commissure,  (d)  A  central  group 
in  the  central  part  of  the  dorsal  cornu,  some  of  the  axones  of  which  may  cross  in 
the  ventral  commissure,  (e)  Basal  cells  in  the  base  of  the  horn  and  in  the  pro- 
cessus reticularis,  the  axones  of  which  usually  go  to  the  lateral  column  but  may 
cross,  (f)  Dorsal  (thoracic)  nucleus  or  cells  of  darkens  column  in  the  mesial  part 
of  the  base  of  the  dorsal  horn.  These  are  tautomeric  cells,  the  axones  of  which 
from  the  dorsal  spino-cerebellar  tract  (see  page  463).  Clarke's  column  is  mainly 
confined  to  the  dorsal  or  thoracic  cord,  but  is  also  present  in  the  first  lumbar 
segment. 

(B)  Cells  or  the  Intermediate  Gray. — (a)  Middle  nucleus  whose  cells 
may  send  their  axones  across  in  the  ventral  commissure  or  uncrossed  to  the  lateral 
column;  (b)  various  small  cells  including  the  accessory  nucleus  near  Clarke's 
column;  (c)  intermedio-lateral  group  which  in  parts  of  the  cord  forms  a  projection 
of  the  gray  known  as  the  lateral  horn.  These  are  probably  root  cells  whose 
axones  pass  as  pregangHonic  fibres  into  the  sympathetic  system.     This  nucleus 


THE  NERVOUS  SYSTEM 


451 


is  more  conspicuous  in  the  thoracic  cord,  but  extends  from  the  seventh  or  eighth 
cervical  to  about  the  third  lumbar  segment  and  is  also  present  in  the  sacral  cord 
(especially  the  third  segment),     (pp.  456,  457  and  458.) 

From  the  above  it  is  seen  that  all  the  cells  of  the  dorsal  and  intermediate 
gray,  except  the  interniedio-lateral  group,  are  column  cells,  either  tautomeric, 
heteromeric  or  hecateromeric. 


■X 

0 

C 

rt 

^  -ji 

■3  V  2 

c3  ca 

0 
'so 
c 
0 

a 

t3 

a 

■Ji 

6" 


(C)  Cells  of  thf.  Vlntral  Worx.— These  fall  into  two  categories:  (i) 
Column  Cells.  These  may  he  tautomeric,  sending  axoncs  to  the  adjoining  while 
matter  or  heteromeric,  the  axones  of  which  cross  in  the  ventral  commissure  to  the 
while  matter  of  the  opposite  side.  Among  I  he  hitter  may  be  a  well-marked  group 
in  the  dorso-mesial  part  of  the  horn  (commissural  nucleus).  Hecateromeric 
cells  may  be  present.  (2)  Root  cells.  Two  main  divisions  may  be  distinguished: 
(a)  Mesial  group,  present  throughout  the  cord  above  the  fifth  sacral  segment 


452  THE  ORGANS 

(Bruce).  This  group  probably  innervates  the  striated  voluntary  (somatic) 
muscles  of  the  trunk.  The  mesial  group  is  in  part  of  the  cord  subdivided  into 
a  ventro-mesial  and  dorso-mesial  group,  the  latter  being  present  in  the  first, 
sixth  and  seventh  cervical,  thoracic  (except  first),  and  first  lumbar  segments, 
(b)  Lateral  group,  present  in  the  cervical,  first  thoracic,  and  lumbo-sacral  re- 
gions. This  group  innervates  the  muscles  of  the  extremities  and  exhibits  the 
following  subdivisions:  An  antero-lateral  (C4  to  C8,  L2  to  S2),  a  postero-lateral 
(C4  to  C8,  L2  to  S3)  and  a  post-postero-lateral  (C8  to  Thi,  Si  to  S3).  There  is 
also  a  central  group  (L2  to  S2)  and  a  small  anterior  group  (Li  to  L4).  The  exact 
muscle  groups  innervated  by  these  cell  groups,  respectively,  have  not  yet  been 
definitely  determined.  Other  special  cell  groups  are  tht  phrenic  group  (C4),  cen- 
trally located,  cilio-spinal  and  other  cells  (C8  to  Th2,  to  sympathetic  ganglia 
which  send  fibres  to  dilator  pupillae  and  blood-vessels  of  head),  and  the  spinal 
accessory  (Ci  to  C6).  The  latter  is  located  laterally  and  innervates  the  sterno- 
mastoid  and  trapezius  muscles.  In  the  lumbo-sacral  cord  below  the  fourth 
lumbar  there  is  also  a  medio-ventral  splanchnic  group  which  together  with  the 
lateral  horn  group  of  the  sacral  cord  furnishes  the  preganglionic  fibres  emerging 
from  the  sacral  cord. 

For  the  determination  of  the  destination  of  the  axones  of  the  efferent  root 
cells  the  method  of  studying  the  changes  in  the  cell  body  (Nissl  stain)  in  definite 
lesions  of  the  peripheral  fibres  (axonal  degeneration,  see  Chapter  VI)  is  used. 

Arrangement  of  Fibres  (Fig.  312). — With  the  low-  and  high-power  objectives 
the  course  of  the  transverse  (j.e.,  longitudinally  cut)  nerve  fibres  should  be  care- 
fully studied  in  Weigert  and  Cajal  preparations.  These  fibres  pass  from  gray 
to  white  matter  or  vice  versa,  and  are  in  general  (a)  root  fibres  entering  or  leaving 
the  cord;  (b)  either  axones  of  column  cells  in  the  gray  passing  out  into  the  white 
there  to  become  longitudinal  fibers  by  turning  or  splitting,  or  they  are  the  col- 
laterals and  terminals  of  the  fibres  of  the  white  matter  entering  the  gray  to 
terminate  there. 

The  arrangement  of  these  fibres  should  be  carefully  studied  in  all  parts  of  the 
section  (Weigert' and  Cajal),  taking  one  field  at  a  time.  In  the  dorsal  part  of  the 
cord,  the  dorsal  roots  can  be  seen  entering.  From  their  lateral  portion  fine 
fibres  detach  themselves  and  enter  the  zone  of  Lissauer,  the  fibres  of  which  are 
largely  composed  of  their  short  ascending  and  descending  arms.  Most  of  the 
fibres  of  the  root  pass  along  the  dorsal  and  mesial  side  of  the  dorsal  horn, 
forming  the  zone  of  entry  of  the  dorsal  roots.  By  bifurcating  (not  visible  in  the 
preparation)  they  become  the  majority  of  the  longitudinal  fibres  of  the  dorsal 
funiculus.  From  the  entering  root  fibres  and  fibres  of  the  dorsal  funiculus, 
bundles  of  fine  fibres  (collaterals  and  terminals)  pass  radially  through  the 
gelatinous  substance  of  Rolando  or  sweep  around  its  mesial  side  and  enter  the 
gray.  Some  of  these  terminate  in  the  gelatinous  substance  of  Rolando  (Golgi 
preparations),  some  form  part  of  the  dense  plexus  of  fibres  in  the  caput  and  ter- 
minate there,  others  can  be  traced  to  the  intermediate  gray  and,  in  some  cases, 
some  ("direct  reflex  collaterals")  can  be  traced  to  the  ventral  horn.  It  will  be 
noted  that  not  many  come  from  the  mesial  part  of  the  dorsal  funiculus.  Col- 
laterals from  the  zone  of  Lissauer  enter  the  gelatinous  substance  of  Rolando. 
In  the  middle  part  of  the  cord  there  is  a  similar  interchange  of  fibres  between 


THE  NERVOUS  SYSTEM 


453 


the  plexus  in  the  gray  and  the  adjoining  white  matter.  In  the  ventral  part  of 
the  cord  a  similar  interchange  takes  place,  but  here  besides  these  fine  fibres  are 
seen  the  coarse  fibres  of  the  ventral  roots  gathered  from  various  parts  of  the 
ventral  horn  to  form  bundles  which  leave  the  ventral  side  of  the  horn,  pass  through 
the  white  matter  and  emerge  as  the  ventral  root  fibres.  The  larger  bundles  o£ 
fibres  in  the  ventral  horn  separate  the  cell  groups,  but  between  individual  cells 
are  seen  numerous  fine  medullated  fibres  (principally  terminals  of  fibres  from  the 
white  funiculi).  Trace  as  far  as  possible  the  course  of  the  fibres  of  the  ventral 
and  dorsal  white  commissures. 

Finer  Structures.' — Study  with  the  high  power  the  general  histological  struc- 
ture of  the  gray  and  white  matter.  In  the  gray  matter  note  (Cajal,  Nissl,  H.-E.) , 
besides  the  nerve  cells  and  their  processes,  the  neuroglia  nuclei.  Note  also  the 
structure  and  size  of  the  medullated  nerve  fibres  (Weigert).     In  the  white  matter 


Fig.  313. — I'rom  Transv^erse  Section  of  Elephant's  Cord. 
Neuroglia  Stain,  b,  c,  d  and  i,  Four  types  of  neuroglia  cells;  k 
through  several  neuroglia  cells;  /,  leucocyte. 


(Hardesty.)     Benda's 
neuroglia  fibre  passing 


note  the  appearance  of  the  cross-cut  medullated  nerve  fibres  in  Weigert,  Cajal 
and  H.-E.  preparations.  With  the  neuroglia  stains  study  carefully  the  neuroglia 
cells  and  neuroglia  fibres,  including  the  neuroglia  zone  forming  the  margin  of  the 
cord.  (Fig.  313.)  Note  also  the  pia  mater  and  the  connective-tissue  septa 
(usually  perivascular)  entering  the  cord  from  the  pia  accompanied  usually  by  a 
denser  aggregation  of  glia  fibres.  Note  carefully  the  number  of  neuroglia  nuclei 
in  some  small  field.  Increase  in  neuroglia  is  characteristic  of  many  pathological 
conditions.     Study  the  ependyma.     (Weigert,  Nissl,  Cajal  and  glia  stains). 

Study  the  internal  structure  of  the  nerve-cells  of  various  sizes  present,  espe- 
cially the  amount  and  arrangement  of  the  chromophilic  substance  (Nissl).  The 
smallest  nerve  cells  of  the  cord  have  a  limited  amount  of  chromophilic  substance, 
often  either  in  the  form  of  perinuclear  cai)s  or  small  bodies  near  the  i)criphery 


*  It  may  sometimes  he  afivantagcous  to  hi 
histological  structure  of  the  gray  and  while  m;i 
architeclural  arrangements  of  the  ar  '  '  ' 


■al 


to  have  iho  high  power  study  of  the  gencru, 

_  ...alter  of  the  cord  precede  the  study  of  the 

ird  here  placed  first. 


454 


THE  ORGANS 


of  the  cell.  In  the  medium  cells  more  chromophilic  bodies  are  present.  The 
ceUs  of  Clarke's  column  have  a  considerable  number  of  chromophilic  bodies 
arranged  near  the  periphery  of  the  cell.  The  root  cells  are  richest  in  chromo- 
philic substance  (for  further  details  see  Chap.  VI).  In  general  it  seems  that 
the  intermediate  neurones  belonging  to  efferent  paths  {i.e.,  acting  on  periph- 
eral motor  neurones)  have  the  definite,  clear-cut.  coarse  chromophilic  granules 
characteristic  of  the  peripheral  motor  neurones;  while  the  neurones  forming 
parts  of  afferent  paths  have  the  fine,  indefinitely  grouped  granules  character- 
istic of  the  cerebro-spinal  ganglionic  neurones  (Jacobsohn  and  Malone) . 

Blood-vessels  (Fig.  3 14. — )Study  the  arrangement  and  structure  of  the  blood- 
vessels of  the  cord  and  pia.  There  are  three  principal  longitudinal  arteries, 
the  anterior  spinal  artery  given  off  from  the  vertebral  arteries  near  their  union 


Posterior  spinal  artery- 


Column  cells 


Region  sup- 
plied by  sulco- 
commissural 
artery 


Root  cells 


Anterior  spinal  artery 
(giving  off  a  sulco-commissural  artery) 


Fig.  314. — Schematic  transverse  section  of  Cord,  Showing  General  Distribution  of 
Blood-vessels  (left)  and  Nerve-cells  (right)  (Bing).  Root-cells;  i,  postero-lateral  group; 
2,  antero-lateral  group;  3,  antero-medial  group;  4,  central  group;  5,  postero-medial 
group.  The  broken  black  lines  on  the  surface  of  the  cord  are  portions  of  the  vascular 
network  in  the  pia  mater. 


into  the  basilar  artery,  and  two  posterior  spinal  arteries,  given  off  also  from  the 
vertebral  arteries.  These  arteries  are  reenforced  by  small  arteries  passing  to  the 
cord  along  the  dorsal  and  ventral  roots  and  form  an  arterial  network  in  the  pia 
mater.  From  the  network  terminal  {i.e.,  non-anastomosing)  branches  enter 
the  cord,  supplying  all  parts  except  the  ventral  horn  and  column  of  Clarke. 
The  latter  are  supplied  by  branches  from  the  anterior  spinal  artery  which  pass 
dorsally  in  the  ventral  sulcus  {sulco-commissural  arteries)  and  enter  the  cord 
alternately  to  right  and  left.  They  then  break  up  into  a  rich  capillary  network 
in  the  ventral  horn,  supplying  also  a  branch  to  the  column  of  Clarke.  The  veins 
of  the  cord  also  form  a  plexus  in  the  pia  mater.  Larger  posterior  median  and  an- 
terior median  veins  can  be  distinguished.  Portions  of  the  above  vessels  can  be 
seen,  cut  in  various  planes  in  the  pia  and  in  the  cord.  The  general  appearance 
and  structure  of  the  blood-vessels,  including  capillaries,  should  be  noted  in  the 
various  methods  of  staining. 


THE  NERVOUS  SYSTEM  455 

Variations  in  Structure  at  Different  Levels 

While  the  general  structure  above  described  obtains  throughout 
the  cord,  the  size  and  shape  of  the  cord,  the  size  and  shape  of  the 
gray  matter,  and  the  relative  proportion  of  gray  matter  and  white 
matter,  vary  in  different  parts  of  the  cord,  which  must  therefore  be 
separately  considered.  These  variations  are  due  to:  (i)  Variations 
in  the  size  of  the  nerves  entering  and  leaving,  which  cause  correspond- 
ing variations  in  the  gray  matter  which  receives  the  afferent  fibres 
and  contains  the  cells  of  origin  of  the  efferent  fibres.  Thus  the 
larger  nerves  of  the  extremities  cause  the  increase  in  size  of  the  gray 
matter  of  the  cervical  and  lumbo-sacral  cord  with  which  they  are  con- 
nected, and  also  an  increase  in  the  dorsal  funiculi.  (2)  A  gradual 
increase  in  the  white  matter  of  the  cord,  as  higher  levels  are  reached, 
due  to  an  increase  in  the  number  of  long  ascending  and  descending 
fibres  to  and  from  the  brain. 

PRACTICAL  STUDY 

Section  through  the  Twelfth  Thoracic  Segment  (Fig.  316). — Note  that  the 
cord  is  smaller  than  in  the  lumbar  enlargement  and  somewhat  flattened  dorso- 
ventrally;  that  the  amount  of  gray  matter  and  white  matter  is  diminished;  that 
both  anterior  and  posterior  horns  are  more  slender,  the  anterior  horn  containing 
comparatively  few  cells.  At  the  inner  side  and  base  of  the  posterior  horn  may  be 
seen  the  group  of  cells  known  as  Clarke's  column  (p.  450).  MeduUated  fibres 
can  be  seen  passing  from  the  dorsal  funiculus  into  Clarke's  column,  where  they 
interlace  among  the  nerve  cells.  These  fibres  are  collaterals  of  the  dorsal  root 
fibres  terminating  in  the  nucleus.  From  the  nucleus  coarser  fibres  can  be  seen 
gathering  at  its  ventral  side  and  thence  passing  outward  to  the  periphery  of  the 
cord  where  they  bend  upward  forming  ihe  beginning  of  the  dorsal  spino-cercbellar 
tract  fsee  p.  46.3). 

Section  through  the  Mid-thoracic  Region  (Fig.  316). — Compare  with  the 
lumbar  sections.  Xote  the  change  in  shape  and  size;  that  the  cord  is  more 
nearly  round  and  smaller;  that  while  the  reduction  in  size  affects  both  gray  matter 
and  white  matter  it  is  the  former  that  shows  the  greater  decrease.  The  horns 
are  even  more  slender  than  in  the  twelfth  thoracic  section,  and  the  anterior 
horn  contains  still  fewer  cells.     Clarke's  column  is  present,  but  not  so  large. 

Section  through  the  Cervical  Enlargement  (Fig.  315). — Note  the  marked  in- 
crease in  Jiizc  of  the  cord,  which  affects  both  gray  matter  and  white  matter.  De- 
pending upon  the  exact  level  at  which  the  section  is  taken,  the  cord  may  be  nearly 
round  or  flattened  donso-vcntrally.  The  posterior  horns  remain  slender  while 
the  anterior  are  much  broader  than  the  posterior  horns.  The  relkidar  process  is 
more  prominent  than  in  any  of  the  previous  sections.  As  in  the  lumbar  cord, 
the  cell  groups  of  the  anterior  horn  arc  numerous  and  well  defined.     .'\  more  or  less 


^56 


THE  ORGANS 


C.Il 


./^ 


0^\ 


!»•' 


cm 


\ 


C.  V 


C.  VI 


C.  VII 


C.  VIII 


Fig.  315. — Transverse  Sections  through  the  Cervical  (II-VIII)  Segments  of  the  Cord. 
Weigert  preparations.     (Rauber-Kopsch.) 


THE  NERVOUS  SYSTEM 


457 


Th.  Ill 


Th.  IV 


Th.  V 


Th.  XII 

Fig.  316. — Transverse  Sections  ihnjUKh  the  Thoracic  (f-XII)  Segmcnls  u{  llic  C  ord. 

Weigcrt  preparations.     (Kaubcr-Koitsch.) 


458 


THE  ORGANS 


L.I 


L.III 


L.IV 


L.  V 


S.I 


S.III 


S.IV 


S.  V 


Fig.  317. — Transverse  Sections  through  the  Lumbar  (I-V)  and  Sacral  (I-V) Segments 
of  the  Cord.     Weigert  preparations.     Rauber-Kopsch.) 


THE  NERVOUS  SYSTEM  459 

definite  septum  divides  the  posterior  column  into  an  inner  part,  the  column  oJGoll, 
and  an  outer  part,  the  column  of  Burdach. 

For  further  variations  and  differences   between  the  segments  of  the  cord, 
compare  Figs.  315,  316  and  317. 

Fibre  Tracts  of  the  Cord 

The  determination  of  the  fibre  tracts  of  the  cord  has  been  accom- 
phshed  principally  by  two  methods:  (i)  The  myelogenetic  method, 
which  is  based  upon  the  fact  that  the  fibres  of  different  systems  ac- 
quire their  myelin  sheaths  at  different  periods  of  embryonic  develop- 
ment. Thus  by  examining  cords  from  embryos  of  various  ages  and 
young  specimens  it  is  possible,  using  a  myelin  stain  (e.g.,  Weigert), 
to  distinguish  different  tracts  by  the  presence  or  absence  of  myeliniza- 
tion  of  their  fibres.  (2)  The  method  of  secondary  or  axonal  degenera- 
tion, based  upon  the  fact  that  a  fibre  separated  from  its  cell  under- 
goes degenerative  changes  and  ultimately  disappears  and  that  the 
cell  body  also  usually  shows  certain  changes  (see  page  140).  The 
fibres  distal  to  the  injury  can  be  distinguished  during  active  degenera- 
tion'by  applying  the  Marchi  stain  (page  34).  After  their  disappear- 
ance, however,  a  negative  picture  is  obtained  by  staining  the  sur- 
rounding normal  fibres  (Weigert) .  The  changes  in  the  cell  bodies 
whose  axones  are  injured  are  distinguished  by  applying  the  Nissl 
stain  (p.  38).  Thus  if  the  cord  is  cut  at  some  particular  level,  at 
any  level  above  the  cut  all  fibres  present  which  originate  from  cells 
below  the  cut  will  show  degeneration  ("ascending"  degeneration), 
while  the  cell  bodies  of  the  cut  fibres  will  show  the  axonal  degenera- 
tion changes.  On  the  other  hand,  at  any  level  below  the  cut, 
fibres  which  originate  from  cells  above  the  cut  will  show  degenera- 
tion ("descending"  degeneration),  while  the  cell  bodies  of  these 
fibres,  located  above  the  cut,  will  exhibit  axonal  degeneration. 
The  indication  this  gives  as  to  the  direction  of  conduction  is 
evident  when  it  is  remembered  that  the  impulse  passes  from  neu- 
rone body  along  the  axone  to  its  termination.  (3)  Atrophy  (von 
Gudden's  method).  This  method  is  based  upon  the  fact  that 
extirf)ation  of  some  part  of  the  nervous  system  in  a  young  animal 
is  followed  by  an  atrophy  of  parts  in  intimate  relation  therewith. 
This  method  only  demonstrates  grosser  changes  than  the  pre- 
ceding, but  on  the  other  hand  whole  conduction  paths  involving 
more  than  one  neurone  rehiy  may  show  changes.  Other  methods  are 
the  method  of  comparative  anatomy,  i.e.,  study  of  the  simi)ler  nervous 


460 


THE  ORGANS 


THE  NERVOUS  SYSTEM  461 

systems  of  lower  forms  and  the  correlated  development  or  absence  of 
related  parts  of  the  nervous  system,  and  the  method  of  physiology,  i.e., 
study  of  the  physiological  eflfects  of  stimulation  or  extirpation  of 
various  portions  of  the  nervous  system  thereby  indirectly  demon- 
strating anatomical  pathways. 

Ascending  Tracts. 

It  will  be  recalled  that  various  groups  or  systems  of  neurones 
(nuclei  and  tracts)  are  linked  together  to  form  conduction  paths 
(p.  421).  In  general  an  afferent  conduction  path  consists  of  (i)  a 
primary  system  (afferent  ganglionic)  whose  central  processes  (afferent 
root  fibres)  end  in  its  terminal  nucleus;  (2)  a  secondary  system 
whose  bodies  constitute  the  terminal  nucleus  of  (i)  and  whose  axones 
form  a  second  ary  tract  and  end  in  a  secondary  terminal  nucleus; 
(3)  the  conduction  path  may  continue  through  tertiary  nuclei  and 
tracts,  etc. 

A .  Tracts  forming  parts  of  afferent  pallial  paths. 

I.  Long  Ascending  Arms  of  Dorsal  Root  Fibres  {Posterior 
Funiculi). — The  origin  of  these  tracts — central  processes  of  the  cells 
of  the  spinal  ganglia — has  been  described  (page  436).  The  distribu- 
tion of  the  posterior  root  fibres  to  the  gray  matter  of  the  cord  was 
noted  in  connection  with  the  study  of  the  lumbar  enlargement  sec- 
tion Tpage  452).  The  general  arrangement  of  these  fibres  in  the 
dorsal  funiculi  remains  to  be  noted. 

Each  successive  dorsal  root  sends  its  fibres  into  the  cord  next  to 
the  dorsal  horn  and  therefore  lateral  to  the  ascending  fibres  from  the 
next  root  below.  Thus  the  fibres  of  the  lower  roots  as  they  ascend 
the  cord  are  gradually  pushed  toward  the  median  line  until  they  finally 
occupy  that  part  of  the  posterior  column  lying  near  the  posterior  sep- 
tum. The  separation  of  the  posterior  column  by  a  connective-tissue 
septum  into  the  column  of  GoU  and  the  column  of  Burdach  occurs 

Fig.  318. — Diagram  of  the  Tracts  of  the  Cord  (Cervical  Region).  Ascending  tracts 
are  shown  on  the  left  side,  and  descending  tracts  on  the  right.  It  will  be  noticed  that 
the  tracts  of  the  cord  arc  roughly  divisible  into  three  concentric  zones:  (i)  A  zone  oc- 
cupying most  of  the  posterior  columns  and  the  perijjheral  i)art  of  the  lateral  columns. 
This  zone  comprises  the  principal  long  ascending  tracts  (beginnings  of  alTerent  supra- 
segmcntal  pathsj.  (2)  The  second  zone  lies  immediately  within  the  first  in  the  lateral 
columns  and  also  occupies  the  peripheral  part  of  the  anterior  columns.  It  comprises  the 
principal  long  descending  tracts  from  various  |)arts  of  the  brain  (terminal  i)ortions  of  ef- 
ferent suprasegmcntal  paths).  (3)  The  third  zone  borders  the  gray  matter  and  includes 
the  ground  or  fundamental  bundles  of  the  cord  (chiefly  sjjinal  intersegmental  libres). 

In  the  figure,  for  nu,  DarkschewUschi  read  neuclcus  of  medial  longitudinal  fasciculus. 


462  THE  ORGANS 

only  in  the  cervical  cord  (Fig.  311  and  315).  Here  the  most  median 
fibres,  i.e.,  those  lying  in  the  column  of  Goll,  are  the  longest  fibres  of 
the  posterior  columns,  having  come  from  the  lower  spinal  ganglia 
(lower  thoracic,  lumbar  and  sacral),  while  the  column  of  Burdach 
(Fig.  311)  consists  of  short  and  medium  length  fibres  (upper  thoracic 
and  cervical  dorsal  root  fibres) .  The  fibres  of  Goll's  column  end 
in  the  nucleus  juniculi  gracilis  or  nucleus  of  the  column  of  Goll  in 
the  medulla  (see  p.  485  and  Fig.  326).  Those  fibres  of  Burdach's 
which  do  not  terminate  in  the  spinal  cord  terminate  in  the  medulla 
in  the  nucleus  funiculi  cuneati  or  nucleus  of  the  column  of  Burdach 
(p.  485  and  Fig.  326).  The  nucleus  gracilis  and  nucleus  cuneatus — ■ 
which  will  be  seen  in  sections  of  the  medulla  (Fig.  326) — thus  serve 
as  terminal  nuclei  for  the  afferent  root  fibres  in  the  columns  of  Goll 
and  those  of  the  columns  of  Burdach  which  do  not  terminate  within 
the  cord.  Inasmuch  as  many  of  the  ascending  arms  are  short,  it  is 
evident  that  only  a  fraction  of  the  dorsal  root  fibres  are  represented 
at  the  higher  levels.  Those  long  arms  which  reach  the  medulla  con- 
stitute the  beginning  of  one  of  the  principal  afferent  cerebral  or  pallial 
pathways.  The  axones  of  the  neurones,  whose  bodies  are  the  nuclei 
of  Goll  and  Burdach,  cross  and  form  the  tract  known  as  the  medial 
fillet  (or  lemniscus),  composing  the  second  system  of  this  path.  The 
fillet  terminates  in  the  thalamus  and  the  path  is  completed  by  a  third 
system  of  thalamo-cortical  neurones  to  the  cortex  palHi,  (probably 
principally  to  the  post-central  area).  This  path  is,  in  brief,  as  fol- 
lows: spinal  ganglionic  (long  ascending  arms  of  dorsal  roots)  -\- 
fillet  -j-  thalamo-cortical  path,  decussating  in  the  medulla  (Fig.  322). 

n.  The  Spino -thalamic  Tract.— This  arises  from  heteromeric  cells 
lying  probably  principally  in  the  dorsal  horn  (groups  c  and  d,  p.  450). 
Their  axones  cross  in  the  ventral  commissure  and  reach  the  opposite 
lateral  funiculus  where  they  ascend  in  a  position  mesial  to  the  ventral 
spino-cerebellar  tract  (see  below).  This  tract  terminates  in  the 
thalamus  whence  the  path  is  completed  by  thalamo-cortical  neurones. 
The  path  is  thus :  spinal  ganghon  (short  arms  and  collaterals  of  dorsal 
roots)  -|-  spinothalamic  -|-  thalamo-cortical  neurones,  three  systems  of 
neurones.  Its  decussation  takes  place  in  the  cord  at  about  the  level 
of  entry  of  the  dorsal  roots  involved.  Associated  with  this  system 
may  be  some  fibres  to  the  superior  colliculus  (spino-collicular  tract). 
(Figs.  318,  319  and  323). 

B.  Tracts  forming  part  of  paths  to  the  cerebellum. 


THE  NERVOUS  SYSTEM 


463 


III.  The  Dorsal  Spino-cerebellar  Tract  {Tract  of  Flechsig, 
Direct  or  Uncrossed  Cerebellar  Tract). — This  tract  Hes  along  the 
dorsal -lateral  periphery  of  the  cord,  being  bounded  internally  by  the 
crossed  pyramidal  tract  (Fig.  311  and  Fig.  318).  The  fibres  of  the 
direct  cerebellar  tract  are  the  axones  of  the  cells  of  Clarke's  column 
(tautomeric  column  cells)  (Figs. 
318,  319  and  323).  These  axones 
cross  the  intervening  gray  matter 
and  white  matter  of  the  same 
side  and  turn  upward  as  the 
direct  cerebellar  tract.  In  the 
medulla  they  form  part  of  the 
restiform  body  or  inferior  cere- 
bellar peduncle  and  pass  to  the 
cerebellum.  Here  they  enter  the 
gray  matter  of  the  vermis  of  the 
same  or  opposite  side,  ending  in 
ramifications  among  the  nerve 
cells.  Some  fibres  either  end  in, 
or  send  off  collaterals  to,  the 
cerebellar  nuclei.  The  tract  first 
appears  in  the  upper  lumbar 
cord,  and  increases  in  size  until  the 
upper  limit  of  Clarke's  column 
has  been  reached  (page  450). 

As  already  noted  above,  some 
fibres  of  the  posterior  root,  or 
their  collaterals,  end  in  the 
column  of  Clarke.  This  path  is 
composed  then  of  two  systems  of 
neurones,  spinal  ganglion  cells 
and  Clarke's  column  cells,  and  is 
uncrossed    (with    the    exception 

that  some  fibres  are  interrupted  in  the  nucleus  lateralis  of  the 
medulla  and  that  some  of  the  fibres  from  the  nucleus  lateralis 
cross).     (Fig.  337.) 

rV.  The  Ventral  Spino-cerebellar  Tract.- — This  tract  lies  along  the 
periphery  of  the  cord,  extending  from  the  anterior  limit  of  the  direct 
cerebellar  to  about  the  exit  of  the  ventral  roots  (Fig.  31 1  and  Fig.  318). 
It  is  probably  ft^rmed  by  axones  whose  cell  bodies  arc  scattered 


Fig.  319. — ^Diagram  showing  Beginnings 
of  Principal  Long  Ascending  Tracts  of  Cord 
and  Termination  of  Lateral  Pyramidal 
Tract.  Each  group  of  neurones  is  repre- 
sented by  one  or  two  neurones,  d.s-c, 
Dorsal  spino-cerebellar  tract;  p,  lateral 
pyramidal  tract;  s-L,  spino-thalamic  tract; 
v.s-c,  ventral  spino-cerebellar  tract;  v.r., 
ventral  root. 


464  THE  ORGANS 

through  the  intermediate  gray  matter,  possibly  group  a  (p.  450  and 
Fig.  311).  Some  fibres  come  from  tautomeric,  others  from  hetero- 
meric  cells,  the  axones  of  the  latter  crossing  in  the  ventral  commis- 
sure. The  tract  first  appears  in  the  upper  lumbar  cord  and  natur- 
ally increases  in  size  as  it  passes  upward.  The  fibres  of  this  tract 
also  end  in  the  vermis  of  the  cerebellum.  They  reach  their  desti- 
nation in  the  cerebellum  by  a  different  route,  ascending  considerably 
farther  than  the  dorsal  spino-cerebellar  fibres  and  then  turning  back 
along  the  outer  side  of  the  superior  cerebellar  peduncle  to  the  ver- 
mis. This  path  is  thus  also  a  two-neurone  path  (spinal  ganghon 
cells  and  spino-cerebellar  neurones)  and  is  partly  crossed  and  partly 
uncrossed.  The  ventral  spino-cerebellar  and  spino-thalamic  tracts 
are  sometimes  referred  to  as  Gower's  tract.  (Figs.  323  and  337.) 

It  seems  probable  that  muscle-tendon  sense  passes  up  the  cord  by  tract  I 
(uncrossed  in  the  cord),  while  pain  and  temperature  pass  up  by  the  spino- 
thalamic tract  (crossed).  The  path  pursued  by  touch  is  more  doubtful  but  it 
may  pass  up  partly  by  tract  I  and  partly  by  ascending  arms  of  varying  lengths 
which  end  in  the  cord  around  heteromeric  column  cells  (thus  partly  uncrossed  and 
partly  crossed  in  the  cord).  This  path  may  join  the  fillet  in  the  medulla.  It 
would  seem  probable  that  the  cerebellar  tracts  convey  stimuli  from  muscle- 
tendon  receptors.  Ascending  paths  may  also  be  formed  by  successive  relays  of 
shorter  tracts  in  the  ground  bundles  of  the  cord  and  the  reticular  formation  of 
the  brain.  This  has  been  especially  claimed  for  the  pain  pathway.  The  afferent 
visceral  path  to  the  pallium  is  not  known. 

Descending  Tracts 

I.  The  Pyramidal  Tracts  {Tractus  Cortico-spinalis,  Cerehro- 
spinalis  or  PalUo-spinalis). — The  cell  bodies  of  the  neurones  whose 
axones  make  up  this  system  are  situated  in  the  cerebral  cortex 
anterior  to  the  fissure  of  Rolando  (precentral  area,  Fig.  357).  Their 
axones  converge  in  the  corona  radiata  and  pass  downward  through 
the  internal  capsule,  pes  peduncuH,  pons,  and  medulla,  sending  off 
fibres  to  the  motor  nuclei  of  the  cranial  nerves.  In  the  medulla 
the  tracts  come  to  the  surface  as  the  anterior  pyramids.  At  the 
junction  of  medulla  and  cord  occurs  what  is  known  as  the  pyramidal 
decussation.  Here  {a)  most  of  the  fibres  of  each  tract  cross  to  the 
opposite  dorso-lateral  region  of  the  cord  and  continue  downward 
as  the  crossed  or  lateral  pyramidal  tract.  This  lies  in  the  dorsal  part 
of  the  lateral  column  (Figs.  311  and  318).  It  extends  to  the  lower- 
most part  of  the  cord.  In  the  cervical  and  dorsal  region  it  is  sepa- 
rated from  the  surface  of  the  cord  by  the  direct  cerebellar  tract.     In 


THE  XERVOUS  SYSTEM  465 

the  lumbar  region  the  latter  tract  is  no  longer  present  and  the  crossed 
pyramidal  tract  comes  to  the  surface,  (b)  The  minority  of  the  fibres 
of  the  anterior  pyramids,  instead  of  decussating,  remain  on  the 
same  side  to  pass  down  the  cord  along  the  anterior  median  fissure 
as  the  direct  or  anterior  pyramidal  tract,  occupying  a  small  oval  area 
adjacent  to  the  anterior  sulcus  (Fig.  318).  It  does  not  usually 
extend  below  the  middle  or  lower  dorsal  region  of  the  cord.  As  the 
pyramidal  tracts  descend  they  decrease  in  size  from  loss  of  fibres 
which  continually  leave  them  to  terminate  in  the  ventral  horn% 
The  fibres  of  the  crossed  tract  terminate  mainly  in  the  horn  of  thor 
same  side,  while  most  of  the  fibres  of  the  direct  tract  probably  croi 
through  the  anterior  commissure  to  the  opposite  side  of  the  corc'^^ 
These  tracts  are  thus  mainly  crossed  tracts,  as  the  great  majorit  ' 
of  their  fibres  cross  to  the  opposite  side  of  the  cord.  There  are^^ 
however,  some  homolateral  (uncrossed)  fibres  in  the  lateral  pyram- 
idal tract.  The  tracts  are  apt  to  differ  in  size  on  the  two  sides  of  the 
cord,  owing  to  the  fact  that  the  proportion  of  fibres  which  decus- 
sate is  not  constant.  The  axones  terminate  in  arborizations  around 
the  motor  cells  of  the  ventral  horns.  The  pyramidal  tracts  or  pallio- 
spinal  system  together  with  the  spinal  efferent  peripheral  neurone 
system  constitutes  the  pallio-spino- peripheral  efferent  conduction  path. 
According  to  some  authorities  the  pyramidal  fibres  terminate  around 
cells  in  the  intermediate  gray  matter  whose  axones,  which  form  a 
part  of  the  ground  bundles,  in  turn  terminate  around  the  eft'erent 
root  cells.  Short  axone  (Golgi  type  II)  cells  might  also  of  course  be 
intercalated  in  this  connection.  (Figs.  322  and  323.) 

The  pyramidal  tracts  convey  to  the  cord  the  impulses  which  result  in  volun- 
tary movements,  especiall)',  probably,  individual  movements  of  parts  of  the 
limbs  (foot,  hand,  finger,  etc.). 

n.  The  Colliculo -spinal  Tract  (Tectospinal  Tract)  orginates  in 
the  colliculi  of  the  midbrain  roof,  decussates  and  descends  to  the  cord, 
where  it  lies  near  the  ventral  sulcus.  Its  presence  in  the  cord  has 
been  disj)uted.     TFig.  350.) 

III.  The  Tract  from  the  Nucleus  of  the  Posterior  or  Medial 
Longitudinal  Fasciculus.— This  nucleus  is  located  in  the  reticular 
formation  of  the  tegmentum  of  the  midbrain  cephalad  to  the  nucleus 
of  nerve  III.^     The  tract  originating  from  it  forms  in  the  brain  a  part 

'  The  fibres  in  question  have  been  variously  slated  to  originate  from  the  nucleus  of 
Darkschewitsch,  the  "nucleus  of  the  posterior  longitudinal  fasciculus,"  and  the  nucleus 
of  the  posterior  commissure.  Whether  any  of  these  nuclei  is  the  same  as  the  inlerslitial 
nucleus  of  Cajal,  or  the  nucleus  of  van  (iehuchten  in  fishes,  is  uncertain.  Hy  the  nucleus 
of  the  medial  longitudinal  fasciculus  is  here  meant  the  interstitial  nucleus  of  Cajal. 
30 


466  THE  ORGANS 

of  the  posterior  or  medial  longitudinal  fasciculus.  It  is  uncrossed 
and  lies  near  the  floor  of  the  brain  cavity  and  next  the  median  line. 
In  the  cord  it  occupies  a  similar  position  near  the  ventral  sulcus. 
Its  fibres  terminate  in  the  ventral  horn.  Some  fibres  have  been 
traced  into  the  lumbar  cord.     (Figs.  318  and  350.) 

IV.  The  Rubro-spinal  Tract  {von  Monakow's  Tract). — This  con- 
sists of  axones  of  the  red  nucleus  (nucleus  ruber)  located  in  the  teg- 

'  mentum  of  the  midbrain.     These  axones  cross  and  descend  to  the 

fa  .       • 

^rd,  being  joined  by  axones  of  the  other  cells  in  the  reticular  forma- 

,  n  in  the  region  of  the  pons.     In  the  cord  the  tract  lies  mingled  with 

ntral  to  the  lateral  pyramidal  tract.     Its  fibres  terminate  in  the 
ceJ  • 

rt  of  the  ventral  horn.     This  tract  is  a  lower  link  in  a  three- 
oath   from  cerebellum  to  cord  composed  as  follows:  (a) 
L  cells  in  cerebellar  cortex  to  nucleus  dentatus  in  cerebel- 
;   axones  of  cells  in  nucleus  dentatus  via  superior  cerebellar 
.-..cle  to  the  nucleus  ruber;  (c)   axones  of  nucleus  ruber  as  the 
xuoro-spinal  tract  to  {d)  efferent  peripheral  neurones  of  cord.     (Figs. 
318,  323  and  337.) 

V.  The  Deitero-spinal  Tract  {V estihulo-spinal  Tract). — This 
tract  originates  from  Deiters'  nucleus  which  lies  in  the  medulla  and 
receives  fibres  from  the  vestibular  division  of  the  acoustic  nerve 
and  also  from  the  cerebellum  (see  below).  It  occupies  the  ven- 
tral and  mesial  periphery  of  the  cord.  The  more  lateral  fibres  are 
uncrossed,  those  near  the  ventral  sulcus  come  from  the  nuclei  of 
both  sides.  Descending  with  these  fibres  are  probably  axones  of 
other  vestibular  terminal  nuclei,  and  of  other  nuclei  in  the  gray  re- 
ticular formation  (reticulo-spinal  fibres)  of  the  medulla.  These  fibres 
all  terminate  in  the  ventral  horn.  Some  fibres  have  been  traced  to 
the  sacral  cord.  Deiters'  nucleus  receives  fibres  from  the  cerebellum, 
and  thus  this  tract  is  a  segment  of  a  second  efferent  cerebellar  path- 
way: {a)  Axones  of  cells  in  cerebellar  cortex  to  nucleus  fastigii  in 
cerebellum;  {h)  Axones  of  cePs  of  nucleus  fastigii  as  the  fastigio- 
bulbar  tract  to  Deiters'  nucleus;  (c)  axones  of  cells  of  Deiters'  nucleus 
as  the  Deitero-spinal  tract  to  {d)  efferent  peripheral  neurones  of 
cord.  According  to  some  authorities  some  fibres  proceed  from 
cerebellum  to  cord  without  interraption  in  Deiters'  nucleus.  (Figs. 
318  and  323.) 

All  the  fibres  of  V  are  sometimes  collectively  called  the  antero- 
lateral descending  tract  or  marginal  bundle  of  Lowenthal. 

Tract  III  and  the  mesial  part  of  V  constitute  the  major  portion  of 


THE  NERVOUS  SYSTEM  467 

the  descending  fibres  of  an  important  bundle  in  the  segmental  brain 
known  as  the  medial  longitudinal  fasciculus. 

VI.  The  Fasciculus  of  Thomas. — Besides  the  reticulo-spinal  fibres  already 
mentioned  are  fibres  in  the  lateral  column  which  originate  in  the  reticular  forma- 
tion of  the  medulla  and  terminate  in  the  gray  of  the  cervical  cord.  These  are 
known  as  the  tract  of  Thomas.     (Fig.  318.) 

VII.  Helweg's  tract  is  a  small  triangular  bundle  of  fibres  lying  along  the 
ventro-lateral  margin  of  the  cord,  and  is  traceable  upward  as  far  as  the  olives 
(Fig.  318).  The  origin  and  destination  of  its  fibres  are  not  definitely  known. 
Some  of  its  fibres  appear  to  originate  in  the  cord  and  terminate  in  the  inferior 
olivary  nucleus  in  the  medulla  (spino-olivary  fibres). 

Vin.  The  Septo-marginal  Tract. — This  is  a  small  bundle  of  fibres  lying  next 
the  posterior  septum.  It  appears  to  change  its  location  in  different  levels, 
e.g.,  in  the  sacral  cord  it  occupies  a  small  dorso-median  triangle,  in  the  lumbar 
region  it  forms  an  oval  bundle  (of  Flechsig)  at  the  middle  of  the  septum  and  a 
superficial  bundle,  in  the  thoracic  and  cervical  cord  its  fibres  are  more  scattered. 
It  is  probably  composed  of  descending  axones  of  cells  in  the  cord.     (Fig.  318.) 

IX.  The  so-called  "comma"  tract  of  Schultze  is  a  small  comma-shaped 
bundle  of  descending  fibres  lying  about  the  middle  of  the  posterior  column  (Fig. 
318).  It  is  most  prominent  in  the  dorsal  cord.  Its  fibres  are  believed  by  some 
to  be  descending  branches  of  spinal  ganglion  cells,  by  others  to  be  descending 
axones  from  cells  situated  in  the  gray  matter  of  the  cord  (column  cells). 

In  general  the  descending  tracts  fall  into  two  categories:  (i) 
Tracts  which  are  descending  or  efferent  suprasegmental  paths,  or  are 
parts  of  such  paths.  These  comprise  (a)  the  efferent  pallial  path 
(tract  I),  (b)  the  efferent  midbrain  paths  (tracts  II  and  III)  and  (c) 
the  efferent  cerebellar  paths  (tracts  IV  and  V).  (2)  Descending  inter- 
segmental tracts.  Of  the  latter  some  originate  in  nuclei  lying  in  the 
segmental  brain  (nucleus  of  the  medial  longitudinal  fasciculus, 
nucleus  ruber,  nucleus  of  Deiters)  which  receive  efferent  supraseg- 
mental fibres,  and  thus  form  links  of  descending  suprasegmental  paths. 
Other  reticulo-spinal  libres  come  from  other  cells  in  the  gray  reticular 
formation.  Other  still  shorter  tracts  (spino-spinal),  from  cells  in  the 
cord,  form  the  descending  fibres  in  the  ground  bundles  (see  below). 
Tracts  VIII  and  possibly  IX  are  also  in  this  category. 

The  descending  j)ath  from  the  i)allium  which  terminates  around 
the  bodies  of  the  splanchnic  efferent  neurones  in  the  cord  is  stated 
to  consist  of  two  neurones,  a  pallio-bulbar  neurone  to  the  medulla  and 
a  bulbo-spinal  neurone  to  the  efferent  perij)heral  neurone  in  the  cord. 
The  axones  of  the  latter  pass  out  of  the  cord  as  preganglionic  fibers 
to  the  sympathetic  ganglion  cells.     In  the  cord  the  fibrt-s  of  this  ]);Lth 


468  THE  ORGANS 

probably  lie  in  the  ventro-lateral  columns,  though  some  authorities 
place  them  in  the  dorsal  columns. 

This  pallio-bulbo-spino-sympathetic  path  is  the  path  by  which  various 
psychic  states  (emotions,  perceptions,  memories)  affect  the  splanchnic  effectors, 
as  seen  in  blushing,  perspiring,  erection,  pupillary  changes,  etc. 

Many  tracts  contain  fibres  proceeding  in  a  direction  opposite  to  that  of  most 
of  the  fibres. 

Fundamental  Columns  or  Ground  Bundles  (Shorter  Inter- 
segmental Tracts  of  Cord  or  Spino-spinal  Tracts) 

The  ascending  and  descending  tracts  above  described  are  known 
as  the  long-fibre  tracts  of  the  cord.  If  the  area  which  these  tracts 
occupy  be  subtracted  from  the  total  area  of  white  matter,  it  is  seen 
that  a  considerable  area  still  remains  unaccounted  for.  This  area 
is  especially  large  in  the  antero-lateral  region,  and  extends  up  along 

Receptor 


Fig.  320. — Diagram  illustrating  a  Two-neurone  Spinal  Reflex  Arc.     Groups  of  neu- 
rones are  represented  by  one  neurone,     gg,  Spinal  ganglion.     (Van  Gehuchten.) 

the  lateral  side  of  the  posterior  horn  between  the  latter  and  the  crossed 
pyramidal  tract  (Figs.  311  and  318).  A  small  area  in  the  posterior 
column  just  dorsal  to  the  posterior  commissure,  and  extending  up  a 
short  distance  along  the  medial  aspect  of  the  horn,  should  also  be 
included.  These  areas  are  occupied  by  the  fundamental  columns  or 
short-fibre  (spino-spinal  or  proprio-spinal)  systems  of  the  cord.     The 


THE  NERVOUS  SYSTEM 


469 


fibres  serve  as  longitudinal  commissural  fibres  to  bring  the  different 
segments  of  the  cord  into  communication  (Fig.  321).  The  shorter 
fibres  lie  nearest  the  gray  matter  and  link  together  adjacent  segments. 
The  longer  fibres  He  farther  from  the  gray  matter  and  continue 
through  several  segments.  The  origin  of  these  fibres  as  axones  of 
cells  of  the  gray  matter,  and  the  manner  in  which  they  re-enter  the 
gray  matter  as  terminals  and  collaterals 
have  been  considered  (pp.  444  and  445)- 

The  fact,  alluded  to  above,  that  the 
shorter  fibres  lie  nearest,  or  mingled  with 
the  gray  is,  in  a  general  way,  true  through- 
out the  central  nervous  system.  A  result 
of  this  in  the  cord  is  the  superficial  posi- 
tion of  many  of  the  longest  tracts. 

Attention  has  already  been  called  to 
the  concept  of  neural  arcs  which  may 
traverse  the  cord  or  both  cord  and 
suprasegmental  structures  (page  421). 

It  must  be  kept  in  mind  that  there  are  prob- 
ably no  isolated  neural  arcs  and  that  every 
neural  reaction  involving  any  given  arc  always 
influences  and  is  influenced  by  other  parts  of 
the  nervous  system. 


Fig.  321. — Diagram  ilhistrat- 
ing  Three-neurone  Spinal  Reflex 
Arcs  of  one  segment  and  more 
than  one  segment.  Groups  of 
neurones  are  represented  by  one 
neurone.  g,  Spinal  ganglion 
cells;  h.c.c,  hetcromeric  column 
cell;  Lc.c,  tautomeric  column 
cell;  v.r.,  ventral  root. 


From  the  neurones  thus  far  studied 
and  the  tracts  which  their  axones  form, 
the  following  neural  arcs  may  be  con- 
structed: 

(i)  A  Two-neurone  Spinal  Reflex  Arc 
(Fig.  320). — (a)  Peripheral  ajjerent  neu- 
rones; their  peripheral  processes  and  receptors,  the  spinal  ganglion 
cells,  their  central  processes  with  collaterals  terminating  around 
motor  cells  of  anterior  horn;  {h)  peripheral  efferent  neurones,  i.e., 
motor  cells  of  anterior  horn  with  axones  passing  to  effectors. 
Such  a  two-neurone  reflex  arc  is  chiefly  uncrossed  and  in  most  cases 
involves  only  one  segment  or  closely  adjacent  segments.  As  it 
involves  only  one  synapsis  (see  chapter  VI)  (in  the  ventral  gray)  it  is 
sometimes  termed  a  monosynaptic  arc. 

(2)  A  Three-neurone  Spinal  Reflex  Arc  (Ing.  321). — {a)  Peripheral 
aferenl  neurones  as  in  (1),  but  terminating  around  column  cells  of  the 
cord,     {b)  Cord  neurones  (column  cells) — axones  in  the  fundamental 


470  THE  ORGANS 

columns  with  collaterals  and  terminals  to  anterior  horn  cells  of 
different  levels,  (c)  Peripheral  efferent  neurones  as  in  the  two-neu- 
rone reflex.  Such  a  three-neurone  or  disynaptic  reflex  arc  may 
involve  segments  above  or  below  the  segment  of  entrance  of  the 
stimulus  and  is  uncrossed  or  crossed  according  as  the  cord  neurones 
are  tautomeric  or  heteromeric. 

The  independence  of  the  cord  as  a  reflex  mechanism  is  much  diminished  in 
man. 

(3)  A  Cerebellar  Arc  may  be  constituted  as  follows:  (a)  Peripheral 
afferent  neurones  to  (h)  column  cells  in  cord  {e.g.,  Clarke's  column) 
via  spino-cerebellar  tracts  to  cerebellar  cortex;  (c)  various  associative 
cortical  cerebellar  neurones;  {d)  axones  of  cortical  cells  to  {e)  dentate 
nucleus  the  axones  of  which  (superior  peduncle)  pass  to  (/")  nucleus 
ruber  via  mbro-spinal  tract  to  {g)  efferent  peripheral  neurones  in 
cord.  Another  arc  would  consist  of  {a),  (b)  and  (c)  the  same,  (d) 
cerebellar  cortex  to  nucleus  fastigii  in  cerebellum  to  (e)  nucleus  of 
Deiters  to  (/")  efferent  peripheral  neurones  to  effectors  (Figs.  323  and 

337)- 

Fig.  322. — Diagram  showing  the  Most  Important  Direct  Paths  which  an  Impulse 
follows  in  passing  from  a  Receptor  (S)  to  the  Cerebral  Cortex  and  from  the  latter  back  to 
an  Effector  {M)  {e.g.,  muscle),  also  some  of  the  cranial-nerve  connections  with  the  cere- 
bral cortex.  Groups  of  neurones  are  represented  by  one  or  several  individual  neurones. 
A,  Sensory  cortex;  B,  motor  cortex;  C,  level  of  third  nerve  nucleus;  D,  level  of  sixth  and 
seventh  nerve  nuclei ;  E,  level  of  fiUet  or  sensory  decussation ;  F,  level  of  pyramidal  or  motor 
decussation;  G,  spinal  cord. 

From  Periphery  to  Cortex. 

Neurone  No.  i. — The  Peripheral  afferent  Neurone:  i,  Spinal,  cell  bodies  in  spinal 
ganglia;  receptor,  S,  peripheral  arm  of  spinal  ganglion  cell;  central  arm  of  spinal  ganglion 
cell  as  fibre  of  dorsal  root  to  column  of  Goll  or  of  Burdach,  thence  to  nucleus  of  one  of 
these  columns  in  the  medulla.  Vi,  Cranial  (example,  fifth  cranial  nerve,  trigeminus; 
ceU  bodies  in  Gasserian  ganglion);  receptor;  peripheral  arm  of  Gasserian  ganglion  cell; 
central  arm  of  Gasserian  ganglion  cell  to  medulla  as  afferent  root  of  fifth  nerve,  thence 
to  terminal  nuclei  in  medulla. 

Neurone  No.  2. — 2,  Spinal  connection — CeU  body  in  nucleus  of  Goll  or  of  Burdach; 
axone  passing  as  fibre  of  fillet  to  thalamus.  V2,  Cranial  nerve  connection  (trigeminal), 
cell  body  in  one  of  trigeminal  nuclei  in  medulla,  axone  as  fibre  of  secondary  trigeminal 
tract  to  thalamus. 

Neurone  No.  3. — 3,  Cell  body  in  thalamus,  axone  passing  through  internal  capsule 
to  termination  in  cortex.     (Various  association  neurones  in  cortex  omitted.) 

From  Cortex  to  Periphery 

Neurone  No.  4. — 4,  Cell  body  in  motor  cerebral  cortex;  axone  through  internal  cap- 
sule and  pes  to  (a)  motor  nuclei  of  cranial  nerves  (Jb)  by  means  of  pyramidal  tracts  to 
ventral  gray  of  spinal  cord. 

Neurone  No.  5. — 5,  Spinal,  cell  body  in  ventral  gray  of  cord;  axone  as  motor  fibre 
of  ventral  root  through  mixed  spinal  nerve  to  effector  (muscle). 

Neurone  No.  5. — Cranial — Vi,  Cell  body  in  motor  nucleus  of  trigeminus;  axone 
passing  to  muscle  as  motor  fibre  of  fifth  nerve. 

Illh,  Peripheral  efferent  neurone  of  third  nerve — oculomotor.  F/5,  Peripheral 
efferent  neurone  of  sixth  nerve — abducens.  Vlh,  Peripheral  efferent  neurone  of 
seventh  nerve — facial.  Xlli,  Peripheral  efferent  neurone  of  twelfth  nerve — hypo- 
glossal. 


THE  NERVOUS  SYSTEM 


471 


(4)  A  Cerebral  or  Pallial  Arc:  (a)  Peripheral  afferent  neurones, 
via  long  ascending  artns  to  (b)  nucleus  gracilis  or  cuneatus,  thence  as 
medial  lemniscus  to  (c) 
thalamus  to  cortex 
pallii;  (d)  associative 
neurones  of  cortex;  (e) 
cortical  precentral  neu- 
rones via  pyramid  to 
(f)  efferent  peripheral 
neurones  to  effectors. 
Another  arc  would  in- 
volve the  spino-thala- 
mic  tract  instead  of  the 
lemniscus .  ( Figs .  322 
and  323.) 

Similar  arcs  may  in- 
clude efferent  sympa- 
thetic neurones.  (See 
pp.  465  and  436.) 

TECHNIC 

(i)  Carefully  remove  the 
cord  (human  if  possible;  if 
not,  that  of  a  large  dog) 
with  its  membranes,  cut 
into  two  or  three  pieces  if 
necessary,  and  lay  on  shee'c 
cork.  Slit  the  dura  along 
one  side  of  the  cord,  lay  the 
folds  back,  and  pin  the  dura 
to  the  cork.  Care  must  be 
taken  to  leave  the  dura  very 
loose,  otherwise  it  will  flat- 
ten the  cord  as  it  shrinks 
in  hardening.  With  a 
sharp  razor  now  cut  the 
cord,  but  not  the  dura,  into 
seg^nents  about  i  cm.  thick. 
Fix  in  Orth's  fluid  (p.  7). 
Pieces  of  the  cord  may  i)e 
cut  out  as  wanted  and  cm- 
bedded  in  cclloidin.  Sec- 
tions shoulrl  be  tut  ai;out 
15/'  in  thickness. 


472  THE  ORGANS 

(2)  For  the  study  of  the  general  internal  structure  of  the  cord,  stain  a  section 
through  the  lumbar  enlargement  of  a  cord  prepared  according  to  the  preceding 
technic  (i)  in  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  21)  and  another 
section  through  the  same  level  in  Weigert's  hasmatoxylin  (technic  p.  32).  Mount 
both  in  balsam.  For  Weigert  staining,  material  fixed  in  formalin  or  in  Orth's 
fluid  should  be  further  hardened  in  MiiUer's  fluid  for  at  least  a  month,  changing 
the  fluid  frequently  at  first  to  remove  the  formalin.  Mallory's  glia  stain  should 
also  be  used  with  material  fixed  in  Zenker's  fluid  (technic,  p.  29).  The  silver 
method  of  Cajal  (alcohol-fixation)  should  also  be  used  (technic,  p.  37)  and  that 
of  Nissl. 

(3)  From  a  cord  prepared  according  to  technic  i,  remove  small  segments 
from  each  of  the  following  levels:  (i)  the  twelfth  dorsal,  (2)  the  mid-dorsal,  and 
(3)  the  cervical  enlargement.  The  segments  are  embedded  in  celloidin,  sections 
cut  15  to  20j«  thick,  stained  by  Weigert's  method  (page  32),  and  mounted  in 
balsam.  Mediillated  sheaths  alone  are  stained  by  this  method  and  appear 
dark  blue  or  black. 

(4)  A  human  cord  from  a  case  in  which  death  has  occurred  some  time  after 
fracture  of  the  vertebras  with  resulting  crushing  of  the  cord,  furnishes  valuable 
but  of  course  rarely  available  material.  If  death  occur  within  a  few  weeks  after 
the  injury,  the  method  of  Marchi  should  be  used ;  if  after  several  weeks,  the  method 
of  Weigert  (page  32).  The  picture  in  the  cord  is  dependent  upon  the  fact  that 
axones  cut  off  from  their  cells  of  origin  degenerate  and  disappear.  After  a  com- 
plete transverse  lesion  of  the  cord,  therefore,  all  ascending  tracts  are  found  de- 
generated above  the  lesion,  all  descending  tracts  below  the  lesion.  The  method 
of  Marchi  gives  a  positive  picture  of  osmic-acid-stained  degenerated  myelin  in 
the  affected  tracts.  The  method  of  Weigert  gives  a  negative  picture,  the  neu- 
roglia tissue  which  has  replaced  the  degenerated  tracts  being  unstained  in  con- 
trast with  the  normal  tracts,  the  myelin  sheaths  of  whose  fibres  stain,  as  usual, 
dark  blue  or  black. 

(5)  Human  cords  from  cases  which  have  lived  some  time  after  the  destruc- 
tion of  the  motor  cortex,  or  after  interruption  of  the  motor  tract  in  any  part  of 
its  course,  may  also  be  used  for  studying  the  descending  fibre  tracts. 

(6)  The  cord  of  an  animal  may  be  cut  or  crushed,  the  animal  kept  alive  for 
from  two  weeks  to  several  months,  and  the  cord  then  treated  as  in  technic  (4). 
The  most  satisfactoiy  animal  material  may  be  obtained  from  a  large  dog  by 
cutting  the  cord  half-way  across,  the  danger  of  too  early  death  from  shock  or 
complications  being  much  less  than  after  complete  section. 

(7)  The  cord  of  a  human  foetus  from  the  sixth  month  to  term  furnishes  good 
material  for  the  study  of  the  anterior  and  posterior  root  fibres,  the  plexus  of 
fine  fibres  in  the  gray  matter,  the  groupings  of  the  anterior  horn  cells,  etc.  The 
pyramidal  tracts  are  at  this  age  non-medullated  and  are  consequently  unstained 
in  Weigert  preparations.  The  cord  of  an  infant  of  about  one  month  is  also  ex- 
cellent. Here  the  majority  of  the  pallio-spinal  fibres  are  medullated  but  very 
thinly  so  that  they  are  easily  distinguishable  by  their  lighter  stain.  The  Wei- 
gert-Pal  method  gives  the  best  results. 

(8)  For  the  study  of  the  course  of  the  posterior  root  fibres  within  the  cord, 
cut  any  desired  number  of  posterior  roots  between  the  ganglia  and  the  cord 


THE  NERVOUS  SYSTEM  473 

and  treat  material  by  the  Marchi  or  the  Weigert  method,  according  to  the  time 
elapsed  between  the  operation  and  the  death  of  the  animal. 

BRAIN 
General  Structure 

The  principal  peculiarities  of  the  brain  as  distinguished  from 
the  cord  depend  upon  two  factors;  certain  pecuKarities  of  the  re- 
ceptors and  effectors  of  the  head  and  the  development  of  higher 
coordinating  apparatus  in  the  central  nervous  system  of  the  head. 

Besides  the  receptors  of  the  general  senses  (p.  436),  there  are  in  the 
head  the  highly  specialized  receptors  of  smell,  sight,  hearing  and  posi- 
tion (semicircular  canals),  which  are  respectively  concentrated  into 
certain  locaKties  and  form,  together  with  certain  accessory  structures, 
the  organs  known  as  the  nose,  eye  and  ear.  Each  of  these  groups  of 
receptors  has  its  own  special  connection  with  the  brain  (nerves  I,  II, 
and  VIII)  and  its  own  paths  within  the  latter  (see  below).  The 
special  receptors  of  taste  show  a  less  degree  of  aggregation  into  an 
organ  and,  together  with  other  visceral  receptors,  are  innervated  by 
afferent  portions  of  a  group  of  nerves  (VII,  IX  and  X)  which  have  a 
common  continuation  within  the  brain.  The  remaining  somatic 
receptors  of  the  general  senses,  scattered  over  the  anterior  part  of  the 
head,  are  innervated  by  one  nerve  (V)  having  its  own  central  con- 
tinuations. It  has  already  been  stated  that  all  the  afferent  periph- 
eral neurones  which  innervate  these  receptors  (except  the  mesen- 
cephalic V)  follow  the  general  law  of  having  their  bodies  located  out- 
side the  neural  tube.  The  central  processes  (root  fibres)  usually  split 
on  entering  the  tube,  but  the  descending  arms  are  the  longer.  Nerves 
I  and  II  present  certain  special  peculiarities. 

The  splanchnic  effectors  of  the  head  include  the  usual  splanchnic 
efifectors — smooth  muscle  and  glands — and  also  the  branchial  stri- 
ated voluntary  muscles.  The  somatic  effectors  are  the  remain- 
ing Tmyotomic)  striated  voluntary  muscles.  The  striated  voluntary 
muscles  of  the  head  fall  into  three  groups;  those  of  the  eye  (somatic); 
of  the  jaw,  face,  pharynx  and  larynx  (splanchnic,  modified  branchial 
musc:ulature);  and  of  the  tongue  (somatic).  The  peripheral  path 
to  the  smooth  muscles  and  glands  follows  the  same  general  law  as  in 
the  body,  i.e.,  neurone  bodies  in  the  central  nervous  system  send  pre- 
ganglionic root  fibres  to  sympathetic  ganglion  cells,  which  in  turn 
send  their  axones  to  the  effectors  (p.  439).     The  peripheral  path  to 


474  THE  ORGANS 

the  splanchnic  (branchial)  striated  voluntary  muscles,  on  the  other 
hand,  follows  the  sam.e  law  as  obtains  for  the  somatic  striated  volun- 
tary muscles,  i.e.,  neurone  bodies  in  the  central  nervous  system  send 
their  efferent  root  fibres  uninterrupted  to  the  muscle.  These  dis- 
tinctions are  shown  centrally  by  differences  in  grouping  of  the  neu- 
rone bodies  which  supply  respectively  the  somatic  muscles,  the 
splanchnic  voluntary  muscles,  and  the  smooth  muscles  and  glands  via 
the  sympathetic  ganglia 

The  higher  coordinating  apparatus'  or  suprasegmental  structures 
(p.  420)  of  the  brain  are  essentially  expansions  of  the  dorsal  walls  of 
parts  of  the  brain,  each  expansion  having  manifold  afferent  and 
efferent  connections  with  the  rest  of  the  nervous  system  and  having 
the  endings  and  beginnings  in  it  of  its  afferent  and  efferent  paths 
complexly  interrelated  by  enormous  numbers  of  association  neurones. 
The  presence  of  these  latter  has  probably  necessitated  the  extensive 
layers  of  externally  placed  neurone  bodies  (cortex)  characteristic 
of  suprasegmental  structures. 

The  structure  of  the  basal  part  of  the  'brain,  connected  with  the 
cranial  nerves  (segmental  brain,  p.  420),  is  affected  by  both  the  pecu- 
liarities of  peripheral  structures  mentioned  above  and  by  the  presence 
of  bundles  of  fibres  and  masses  of  gray  forming  portions  of  paths  to 
and  from  suprasegmental  structures  (see  below). 

The  following  summary  embodies  the  resulting  general  structural 
features  of  the  brain: 

Segmental  Brain  and  Nerves 

Afferent  Peripheral  (Segmental)  Neurones. — (i)  Splanchnic 
Group  comprising  nerves  VII  (geniculate  ganglion),  IX  (superior  and 
petrosal  ganglia)  and  X  (jugular  and  nodose  gangha).  The  nerves 
of  taste  probably  belong  entirely  to  this  group.  The  peripheral 
arms  of  these  ganglia  innervate  visceral  receptors  and  the  central 
arms  form  a  descending  tract  in  the  medulla,  the  fasciculus  solitarius, 
which  has  its  terminal  nucleus  giving  rise  to  secondary  tracts. 

(2)  General  Somatic  Group  (common  or  general  sensibiHty). — 
Semilunar  ganglion  of  V.  The  peripheral  arms  of  the  semilunar 
ganglion  cells  pass  to  the  skin  of  the  anterior  part  of  the  head,  to  the 
mouth  and  meninges.  The  central  arms  of  the  ganglion  cells  form  a 
descending  tract  in  the  medulla,  the  radix  spinalis  V.  The  terminal 
nucleus  of  this  tract  is  the  continuation  in  the  medulla  of  the  dorsal 


THE  NERVOUS  SYSTEM  475 

horn.  The  axones  of  the  terminal  nucleus  form  a  secondary  tract  to 
the  thalamus  and  thence  a  tertiary  thalamo-cortical  tract  passes  to 
the  central  cortex  cerebri.  Axones  of  the  mesencephalic  nucleus  of 
nerve  V  innervate  the  muscle-tendon  receptors  of  the  jaw  muscles 
and  nerves  III,  IV  and  VI  probably  contain  fibres  to  the  muscle- 
tendon  receptors  of  the  eye  muscles. 

(3)  V estibulo-Semicircular  Canal  Group. — GangHon  of  Scarpa  of 
VIII.  The  peripheral  arms  pass  to  vestibule  and  semicircular 
canals.  The  central  arms  constitute  the  vestibular  portion  of  VIII, 
forming  descending  tracts  in  medulla  and  terminating  in  several 
vestibular  terminal  nuclei  (including  Deiters'  nucleus). 

(4)  Acoustic  Group. — Ganglion  spirale  of  VIII.  The  peripheral 
arms  terminate  in  the  organ  of  Corti  of  the  cochlea.  The  central 
arms  form  the  cochlear  part  of  VIII  and  terminate  in  the  medulla 
in  various  nuclei  which  originate  the  secondary  tract  (lateral  fillet) 
to  the  midbrain,  and  medial  geniculate  body  in  thalamus.  A  third 
(or  fourth?)  system  of  thalamo-cortical  neurones  passes  to  the 
temporal  cortex  cerebri  (also  p.  582). 

(5)  Visual  Group. — Ganghon  in  retina.  The  second  neurone 
system  begins  in  the  retina  and  forms  the  secondary  tract  (optic 
"nerve")  to  the  lateral  geniculate  body  in  thalamus.  The  third 
thalamo-cortical  neurone  system  passes  to  the  calcarine  cortex 
cerebri  (also  p.  561). 

(6)  Olfactory  Group. — "  Ganglion"  cells  in  olfactory  mucous  mem- 
brane form  the  olfactory  nerve  (fila  olfactoria)  which  terminates 
in  the  olfactory  bulb.  Secondary  tracts  from  the  olfactory  bulb 
(and  tertiary  tracts)  proceed  to  diencephalon  and  hippocampus 
(also  p.  585). 

Efferent  Peripheral  (Segmental)  Neurones. — (i)  Splanch- 
nic, (a)  Lateral  nuclei  in  the  gray  matter  of  the  hindbrain.  Their 
axones  pass  to  the  striated  voluntary  muscles  of  the  jaw  (V),  face 
(VII),  pharynx  and  larynx  (IX  and  X).  (b)  Nuclei  more  deeply 
placed  in  the  gray  of  mid-  and  hindbrain.  Their  axones  pass  as 
preganglionic  fibres  to  sympathetic  ganglia  of  head  and  body. 
(c)  Sympathetic.  'J'heir  bodies  compose  the  sympathetic  ganglia 
of  the  head  (ciliary,  sphenoi)alatine,  submaxillary  and  otic).  These 
ganglia  receive  the  above  preganglionic  fibres  and  are  thus  connected 
with  cranial  nerves  III,  V,  VII,  IX,  and  X. 

(2)  Somatic. — Medial  nuclei  located  near  the  median  line  in  the 
gray  matter  of  hindbrain  (XII  and  VI),  and  midbrain  (IV  and  III),  to 


476  THE  ORGANS 

muscles  of  tongue  (XII)  and  eye  (VI,  IV  and  III) .  Nerve  III  also 
contains  splanchnic  neurones  whose  axones  pass  to  sympathetic 
ganglia  (ciliary).  Nerves  III,  IV  and  VI  probably  also  contain 
afferent  nerve  fibres  (p.  474,  (2)). 

Intrasegmental  and  Intersegmental  Neurones. — These  are 
represented  principally  by  the  gray  reticular  formation  of  the 
hindbrain  and  midbrain  and  long  descending  tracts  external  to  it. 
The  gray  reticular  formation  is  composed  of  neurone  bodies  and  short 
intersegmental  tracts  intermingled.  Among  the  former  are  certain 
well  differentiated  nuclei  {e.g.,  nucleus  ruber,  nucleus  of  Deiters, 
and  nucleus  of  the  medial  longitudinal  fasciculus)  the  axones  of 
which  form  long,  principally  descending,  intersegmental  tracts 
external  to  the  gray  reticular  formation.  These  may  also  be  links 
in  efferent  suprasegmental  paths.  (See  also  p.  477B,  XIV,  XVI, 
XVII  and  XVIII.)  Other  cells  in  the  gray  reticular  formation  form 
the  shorter  tracts  within  it.  The  reticular  formation  may  also  con- 
tain motor  nuclei  of  the  cranial  nerves  and  is  traversed  by  various 
fibres  passing  to  tracts  and  by  terminals  from  tracts. 

Apeerent  and  Efferent  Suprasegmental  Paths 

These  paths  are  paths  from  receptors  of  body  and  head  to  cere- 
bellum, midbrain  roof  (colliculi)  and  pallium  and  paths  from  cere- 
bellum, midbrain  roof  and  pallium  to  effectors  of  head  and  body. 
There  are  also  paths  connecting  pallium,  mid-brain  roof  and 
cerebellum. 

Afferent  Suprasegmental  Paths 

A .  A  -ff event  Pallial 

I.  General  Somatic  Sensation:  Spinal  and  trigeminal  ganglionic  -|-  spino- 
thalamic and  bulbo-thalamic  (medial  fillet)  crossed  -|-  thalamo-pallial  (to  post- 
central cortex)  neurones.     (Fig.  322.) 

II.  Visceral  Sensation,  including  Taste.  This  important  path  is  not  well 
known.  The  gustatory  path  enters  by  ganghonic  neurones  of  nerves  V  (?), 
IX  and  X  (fasciculus  solitarius) .  Its  secondary  tract  may  lie  partly  in  the  medial 
fiUet. 

III.  Hearing  (cochlear):  Spiral  ganglionic  +  lateral  fillet  (crossed)  and 
brachium  of  inferior  coUiculus  -f-  geniculo-pallial  (to  temporal  cortex)  neurones 
(Fig.  330). 

IV.  Vestibular:  A  somewhat  doubtful  path  except  perhaps  to  the  pallium 
through  the  cerebellum  (paths  X  -f  VII). 


THE  NERVOUS  SYSTE]\r  477 

V.  Sight:  Retinal  bipolar  ganglionic  +  retino-geniculate  (optic  nerve  and 
tract,  crossed  and  uncrossed  in  chiasma)  +  geniculo-pallial  (to  calcarine  cortex) 
neurones.     (Fig.  350.) 

\'I.  Smell:  Olfactory  ganglionic  +  bulbo-rhinencephalic-pallial  (crossed  and 
uncrossed  to  hippocampal  cortex)  neurones.     (Fig.  351.) 

VII.  Cerebello-pallial:  Cerebellar  cortical  +  dentato-rubral  and  dentato- 
thalamic  (superior  cerebellar  peduncle,  crossed)  +  rubro-thalamo-pallial 
neurones.  (Fig.  337.) 

B.  Afferent  Mesencephalic 

VIII.  A  comparatively  unimportant  path  composed  of  spinal  ganglionic 
+  spino-collicular  (crossed)  and  bulbo-collicular  (?  medial  fillet,  crossed) 
neurones. 

C.  Afferent  Cerebellar 

IX.  The  spinal  ganglionic  (innervating  proprioceptors  of  body)  +  spino- 
cerebellar path  to  vermis  of  cerebellum.  The  dorsal  spino-cerebellar  and  ventral 
spino-cerebellar  tracts  of  this  path  pursue  somewhat  different  routes.  (Figs. 
323  and  337.)  This  path  may  receive  accessions  from  the  columns  of  GoU  and 
Burdach  and  their  nuclei  in  the  bulb. 

X.  The  vestibular  ganglionic  (Scarpa)  -f  Deitero-cerebellar  path.  The 
vestibular  ganglionic  neurones  may  send  axones  to  the  cerebellum  without  inter- 
ruption. (Figs.  323,  331  and  337.)  Paths  via  other  cranial  nerves,  especially 
nerves  V  and  II,  may  also  pass  to  the  cerebellum. 

Olivo-cerebellar  neurones  form  part  of  another,  not  well  known,  afferent 
cerebellar  path. 

Efferent  pallial  path  XIII  is  obviously  also  an  afferent  cerebellar  path. 

Erf erent  Suprasegmental  Paths 

A .  Efferent  Pallial 

XI.  \'oluntary  Motor:  Pallio  (precentral  cortex)  —  spinal  (crossed)  +  spinal 
peripheral  somatic  motor  neurones,  also  paUio-tegmental  and  pallio-bulbar 
(crossed  and  uncrossed)  +  cranial  peripheral  somatic  motor  and  branchiomotor 
neurones.  A  short  intersegmental  system  probably  is  intercalated  between 
the  pallial  and  peripheral  neurone  systems.     (Figs.  322,  323.) 

XII.  Splanchnic  Efferent  (except  branchiomotor):  This  is  the  pallio-bulbo- 
spino-sympathctic  path  mentioned  on  page  467  and  comprises  also  descending 
pallial  fibres  which  act  upon  neurones  in  the  brain  whose  axones  pass  out  as 
cranial  preganglionic  fibres. 

XIII.  Pallio-cerebcJlar:  I'allio-{)ontile  +  ponto-cerebelhir  (middle  cere- 
bellar j>eduncle,  crossed)  neurones.     (Figs.  323,  337.) 

XIV.  Pallio-rubral  -|-  rubro-spinal  (crossed)  +  peripheral  motor  neurones 
(p.  512).     This  path  may  [)arlly  supplement,  physiologically,  i)ath  XI. 

Other  less  important  paths  are  mentioned  on  p.  523. 


478  THE  ORGANS 

B.  Efferent  Mesencephalic 

XV.  Colliculo-bulbar  and  coUiculo-spinal  (crossed)  +  cranial  (especially  VII 
for  squint  reflex)  and  spinal  peripheral  motor  neurones.     (Fig.  350.) 

XVI.  CoUiculo-medial  longitudinal  fasciculus:  This  path  probably  consists 
of  coUicular  neurones  which  pass  to  the  nucleus  of  the  medial  longitudinal  fascic- 
ulus +  the  latter  nucleus  and  its  descending  axones  in  the  medial  longitudinal 
fasciculus  +  peripheral  motor  neurones  of  brain  (especially  oculomotor)  and 
cord.     (Fig.  350.) 

Inasmuch  as  the  superior  coUiculus  receives  optic  fibres,  paths  XV  and  XVI 
are  probably  largely  concerned  in  optic  reflexes. 

'  C.  Efferent  Cerebellar 

XVII.  Cerebellar  cortico  (cortex  of  cerebellar  hemispheres)  —  dentate  + 
dentato-rubral  (superior  cerebellar  peduncle,  crossed)  +  rubro-spinal  (crossed) 
+  peripheral  motor  neurones.     (Figs.  323,  337.) 

XVIII.  Cerebellar  cortico  (cortex  of  vermis)— fastigial  +  fastigio  — Deiters 
(mesial  part  of  inferior  cerebellar  peduncle)  +  Deitero-bulbar  and  Deitero-spinal 
(crossed  and  uncrossed)  +  peripheral  oculomotor  and  spinal  motor  neurones. 
(Figs.  323,  331  •) 

Inasmuch  as  Deiters'  nucleus  also  receives  directly  vestibular  nerve  fibres, 
there  exists  the  important  vestibulo-Deiters  +  Deitero-bulbar  and  Deitero-spinal 
+  peripheral  motor  neurones  reflex  path  whereby  the  vestibulo- semicircular  canal 
receptors  directly  influence  the  position  of  eyes  and  body. 

Afferent  pallial  path  VII  is  obviously  also  an  efferent  cerebellar  path.     (Figs. 

323,  337-) 

The  large  efferent  pallial  paths  XI  and  XIII  markedly  affect  the  configura- 
tion of  the  brain.  These  two  paths  are  added  ventrally  to  the  segmental  and 
intersegmental  apparatus  and  form  the  pes  pedunculi  or  crusta  (added  ventrally 
to  the  tegmentum  of  the  midbrain),  the  pons  Varolii  (added  ventrally  to  the  teg- 
mentum of  midbrain,  isthmus  and  hindbrain)  and  the  pyramids  (added  ventrally 
to  the  hindbrain).  Arising  from  the  neopallium  (p.  532),  they  are  to  be  regarded 
as  largely  more  recent  acquisitions  by  the  vertebrate  nervous  system. 

SUPRASEGMENTAL    STRUCTURES 

These  are  the  pallium  or  cerebral  hemispheres,  the  inferior  and 
superior  colHculi  or  corpora  quadrigemina  and  the  cerebellum. 
They  consist  essentially  of  the  endings  and  beginnings  of  their  re- 
spective afferent  and  efferent  paths  and  of  their  own  association 
neurones,  the  bodies  of  which  lie  in  their  respective  cortices. 

The  corpora  quadrigemina  are  relatively  of  much  less  importance  in  the 
human  brain. 

In  accordance  with  the  above  there  are  usually  to  be  distinguished 
in  transverse  sections  of  the  brain  at  various  levels  the  following: 


THE  NERVOUS  SYSTEM  479 

A.  Peripheral  {segmental)  neurones,  (i)  Efferent  ("motor"  nuclei 
and  root  fibres) . 

(2)   Central  continuations  of  afferent  neurones  (afferent  roots). 

(a)  Those  entering  at  and  therefore  belonging  to  the  segment  involved, 

(b)  Those  entering  above  or  below  the  segment  and  represented  in 
the  segment  by  descending  or  ascending  (overlapping)  tracts. 

B.  Terminal  nuclei  of  (2)  and  the  secondary  tracts  originating  from 
them.     These  may  fall  under  category  C  or  D  (below) . 

C.  Intrasegmental  and  Intersegmental  nuclei  and  tracts  of  the  seg- 
mental brain,  consisting  principally  of  the  gray  reticular  formation 
and  long  descending  tracts  (arrangement  much  modified  in  forebrain). 

D.  Nuclei  and  tracts  forming  parts  of  afferent  and  efferent  supra- 
segmental  paths.  The  aft'erent  paths  include  some  of  the  nuclei  and 
tracts  under  B,  and  their  continuations,  and  the  efferent  include  some 
of  the  longer  systems  under  C,  together  with  efferent  suprasegmental 
tracts  to  them. 

E.  Suprasegmental  structures  (not  present  in  many  transections). 
The  general  histology  of  the  brain  is  similar  to  that  of  the  cord. 

Cells  of  the  motor  cranial  nuclei  have  an  arrangement  of  chromophihc 
substance  similar  to  their  analogs  in  the  cord,  while  cells  of  afferent 
cranial  gangha  present  a  chromophihc  picture  similar  to  their  cord 
analogs.  Certain  cells  whose  axones  act  directly  upon  motor  cells 
in  cord  and  brain  {e.g.,  cells  in  motor  cortex  and  certain  cells  in 
reticular  formation)  resemble  motor  cells,  in  arrangement  of  chromo- 
phihc substance,  while  certain  cells  in  close  connection  with  afferent 
peripheral  neurones  resemble  the  latter.  The  neuroglia  cells  and 
fibres  also  present  the  same  general  characteristics  as  those  in  the 
cord,  with  variations  peculiar  to  certain  localities  {e.g.,  parts  of  the 
cerebellum) . 

Hindbrain  or  Rhombencephalon 

This  includes  the  medulla,  cerebellum  and  part  of  the  tegmentum 
and  pons.  Its  peripheral  nerves  are  the  V,  VI,  VII,  VIII,  IX,  X, 
andXII.i 

The  Medulla  Oblongata  or  Bulb  is  the  continuation  upward 
of  the  spinal  cord  and  extends  from  the  lower  Umit  of  the  pyramidal 
decussation  below  to  the  lower  margin  of  the  pons  above. ^ 

'  It  is  better  probably  to  reckon  the  so-called  medullary  or  hulhur  p.irl  of  iheXI  with 
theX. 

*  Jt  would  be  better  to  include  in  the  term  medulla  ohlonj^'aLa  wlial.  here  falls  under 
pontile  tej^mentum  of  the  hindbrain. 


480 


THE  ORGANS 


N.VEST. 

N.cocri. 


RAO.    ANT. 


Fig.  323. 


THE   NERVOUS   SYSTEM  481 

Externally,  the  medulla  shows  the  continuation  upward  of  the 
anterior  fissure  and  posterior  septum  of  the  cord.  On  either  side  of 
the  anterior  fissure  is  a  prominence  caused  by  the  anterior  pyramid, 
and  to  the  outer  side  of  the  pyramid  the  bulging  of  the  olivary  body 
may  be  seen.  The  antero-lateral  surface  of  the  medulla  is  also 
marked  by  the  exit  of  the  fifth  to  the  twelfth  (inclusive)  cranial 
nerves.  The  VI  and  XII  (somatic  motor)  emerge  near  the  mid- 
ventral  line,  the  others,  including  the  splanchnomotor  portions  of  the 
V,  VII,  IX  and  X,  emerge  more  laterally.  The  posterior  surface 
shows  two  prominences  on  either  side.  The  more  median  of  these, 
known  as  the  dava,  is  caused  by  the  nucleus  gracilis,  or  nucleus  of 
the  column  of  Goll;  the  other,  the  cuneus,  lying  just  to  the  outer  side 
of  the  clava,  is  due  to  the  nucleus  cuneatus  or  nucleus  of  the  column 
of  Burdach.  Lateral  to  this  is  a  third  eminence,  the  tuherculum 
cinereum,  due  in  part  to  the  descending  root  of  the  V  and  its  underlying 
terminal  nucleus,  the  continuation  of  the  dorsal  gray  column  of  the 
cord.  This  eminence  merges  anteriorly  with  the  eminence  of  the 
restiform  body.  The  central  canal  of  the  cord  continues  into  the  me- 
dulla, where  it  gradually  approaches  the  dorsal  surface  and  opens  into 
the  ca\dty  of  the  fourth  ventricle.  The  floor  of  the  fourth  ventricle 
exhibits  a  medial  eminence  {trigonum  hypoglossi)  occupied  caudally 
by  the  nucleus  hypoglossi.  Lateral  to  this  is  a  triangular  area,  the 
ala  cinerea  {trigonum  vagi),  surrounded  by  furrows.  This  is  partly 
occupied  by  nuclei  of  the  vagus.     Cephalad  and  laterally  a  broader 


Fig.  323. — Principal  afferent  and  efferent  suprasegmental  pathways  (excepting  the 
rhinopallial  connections,  the  efferent  connections  of  the  midbrain  roof  and  the  olivo- 
cerebellar connections).  EfTerent  peripheral  neurones  of  cranial  nerves  are  omitted. 
Each  neurone  group  (nucleus  and  fasciculus)  is  indicated  by  one  or  several  individual 
neurones.  Decussations  of  tracts  arc  indicated  by  an  X.  ac.  Acoustic  radiation,  from 
medial  geniculate  body  to  temporal  lobe;  hr.  conj,  brachium  conjunctivum  (superior 
cerebellar  peduncle);  br.  ponlis,  brachium  pontis,  from  pons  to  cerebellum;  h.q.i, 
brachium  quadrigeminuminfcrius;  c.^'./,  lateral  or  external  geniculate  body;  c.g.m,  medial 
or  internal  geniculate  body;  c.qiiad,  corpora  quadrigemina; /.cor/. -5/),  pallio-spinal  fascic- 
ulus (pyramidal  tract);  f.c.-p.f,  frontal  pallio-pontile  fasciculus  (from  frontal  lobe); 
f.c.-p.t,  temporal  pallio-ponlilc  fasciculus  (from  temporal  lobe);  f.c.-p.o,  occipital 
pallio-pontile  fasciculus  (from  occipital  lobe); /.am,  fasciculus  cuneatus  (column  of 
Hurdach;;  l.f.-b,  fastigio-bulbar  tract;/,  grar,  fasciculus  gracilis  (column  of  Goll);  f.s.-t, 
>pino-thalamic  fasciculus;  f.sp.-c.d,  dorsal  spino-ccrebellar  fasciculus  (tract  of  Flcchsig) ; 
f.sp.-c.v,  ventral  spino-cerebellar  fasciculus;  km.  lat,  lateral  lemniscus  or  lateral  lillet; 
Irm.  tnrii,  medial  lemniscus  or  fillet;  n.  cocli,  cochlear  nerve;  n.cun,  (terminal)  nucleus  of 
the  column  of  Hurdach;  n.d,  nucleus  of  Dcitcrs;  n.dcnl,  nucleus  dentatus;  n.grac,  nucleus 
of  the  column  of  (ioli;  n.opt,  optic  nerve;  w.r,  nucleusuber;  n.l,  nucleus  tecti  (or  fastigii); 
tt.lri^,  trigeminal  nerve;  n.vest,  vestibular  nerve;  prs.pcd,  j)es  pcdunculi  (crusta);  piilv 
thai,  [)ulvinar  thalami;  pyr,  pyramid;  rod.  anl,  ventral  spinal  root;  rad.  post,  dorsal  sjiinal 
root;  rad.  opt,  of)tic  radiation  (from  lateral  geniculate  body  to  calcarine  region);  iow  ff5. 
I>undles  from  thalamus  to  jjostcentral  region  of  neo|)allium;  .s/>.  i^ang,  spinal  ganglion; 
l.f.-b.,  traclus  fastigio-bulbaris;  thai,  thalamu.s;  l.n.d,  tract  from  the  nucleus  of  Deiters; 
/.  rub.-sp,  rubro-spinal  tract  (von  Monakow).     (Lateral  view  of  brain.) 


482 


THE  ORGANS 


triangular  area  with  an  angle  directed  into  the  lateral  recess  marks 
the  area  occupied  by  the  nuclei  of  the  acoustic  nerve  {area  acustica) . 
Still  further  cephalad  near  the  median  line  are  eminences  indicating 
the  positions  of  the  nucleus  abducentis  and  genu  facialis.  The  roof 
of  the  fourth  ventricle  is  formed  by  the  thin  plexus  chorioideus  and 
the  cerebellum.  (Fig.  324.) 

The  Pons  is  a  mass  of  fibres  and  gray  matter  extending  across  the 
ventral  surface  of  portions  of  mid-  and  hindbrain.     The  term  is  often 


Corp.  mamillaria 

Corp.  pineale 

Colliculus  sup. 

Colliculus  inf. 


Etninentia  med. 
Olive  (in  A) 
Area  acustica  (in  B) 

Eminentia  med. 
Ala  cinerea 


Clava 
Dec.  pyramids  1   . 
Tub.  cuneatum  J 
Tub.  cinereum 


Fig.  349 
Fig.  348 


Fig.  326 
Fig.  32s 


Fig.  324. — Ventral  (A)  and  dorsal  (B)  views  of  part  of  Brain  Stem  (cerebellum 
removed) .  Structures  named  at  the  left  are  indicated  by  their  reference  lines  running  to 
an  X.  On  the  right  are  named  the  figures  showing  transverse  sections  through  the  brain 
at  the  levels  indicated  by  the  reference  lines.  The  level  for  Fig.  349  is  not  quite 
accurately  indicated. 

used  to  include  the  whole  of  the  basal  part  of  the  brain  thus  covered 
by  the  pons.  It  is  better,  however,  to  restrict  it  to  the  pons  itself. 
The  part  of  the  hindbrain  dorsal  to  the  pons,  which  is  the  continua- 
tion forward  of  the  medulla,  may  be  included  in  the  term  tegmentum 
of  the  hindbrain. 

The  Cerebellum  is  described  on  p.  507. 


TECHNIC 

The  technic  of  the  medulla  (and  the  rest  of  the  segmental  brain)  is  the  same 
as  that  of  the  cord  (page  471).  Transverse  sections  should  be  cut  through  the 
following  typical  levels,  stained  by  Weigert's  method  (page  32),  and  mounted 
in  balsam: 


THE  NERVOUS   SYSTEM  483 

1.  Through  the  pyramidal  decussation. 

2.  Through  the  sensory  decussation. 

3.  Through  the  lower  part  of  the  olivary  nucleus. 

4.  Through  the  middle  of  the  olivary  nucleus. 

5.  Through  the  entrance  of  the  cochlear  nerve. 

6.  Through  the  entrance  of  the  vestibular  nerve. 

7.  Through  the  roots  of  the  sixth  and  seventh  cranial  nerves. 

8.  Through  the  roots  of  the  fifth  cranial  nerve. 

The  methods  of  Nissl,  Cajal  and  glia  stains  should  also  be  used  when  practic- 
able. 


PRACTICAL  STUDY 

I.  Transverse  Section  of  the  Medulla  through  the  Decussation  of  the  Pyram- 
idal Tracts  (Motor  Decussation)   (Figs.  324  and  325) 

The  most  conspicuous  features  of  this  section  are  the  decussation  of  the  pyra- 
mids, the  larger  size  of  the  dorsal  horn  and  the  beginning  of  the  gray  reticular 
formation.     Surrounding  the  centra'  canal  is  the  central  gray. 

Efferent  Peripheral  Nevirones. — Nuclei  of  first  cervical  spinal  nerve  in  ventral 
gray,  and  root  fibers  passing  out  to  emerge  on  ventral  aspect.  Nuclei  of  XI,  in 
mesial  position  in  central  gray,  or  in  ventral  gray.  Axones  pass  out  laterally 
from  latter  and  emerge  on  the  lateral  surface.  The  mesial  or  deep  nuclei  are 
best  reckoned  with  nerve  X. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — Some  afferent 
fibres  of  the  first  cervical  spinal  nerve  are  still  entering  at  this  level. 

Ascending  afferent  roots:  The  dorsal  funiculus  comprising  the  fasciculus 
cuneatus  and  fasciculus  gracilis  remain  as  in  the  cord.  Collaterals  and  terminals 
from  them  can  be  seen  entering  the  subjacent  gray. 

Descending  afferent  roots:  Some  of  the  fine  fibres  between  the  enlarged  dorsal 
horn  and  the  periphery,  occupying  the  position  of  the  zone  of  Lissauer  in  the 
cord,  are  descending  afferent  root  fibres  of  the  V-cranial  nerve  or  tractus  spinalis 
trigemini  {spinal  V).  Collaterals  and  terminals  from  these  fibres  terminate  in 
the  gelatinous  substance  of  Rolando  and  also  traverse  it  to  form  a  plexus  of 
medullated  fibres  in  its  inner  side  very  similar  to  the  cord.  The  axones  of  the 
dorsal  horn  cells  (or  terminal  nucleus  of  the  V)  form  the  secondary  tracts  of  the 
V  which  cannot  be  distinguished  (p.  506  and  Fig.  336). 

Secondary  tracts,  forming  parts  of  afferent  suprascgmental  paths:  These  form 
a  mass  of  fibres  along  the  lateral  periphery  of  the  medulla  which  consists  of  (a) 
the  dorsal  spino-Cirrebellar  (b)  the  ventral  spino-cerebellar  and  (c)  the  spino- 
thalamic tracts. 

Intersegmental  Neurones. — The  neurone  bodies  are,  as  in  the  cord,  scattered 
throughout  the  gray.  The  continuation  of  the  ventro-latcral  intersegmental 
tracts  of  the  cord  (and  the  coiliculo-spinal  tract)  is  the  U-shaped  mass  of  fibres 
around  the  ventral  gray.  This  mass  consists  of  the  long  descending,  the  shorter 
ascending  and  descending  intersegmental  tracts,  and  the  coUiculo-spinal;  i.e., 
(a)  rubro-spinal  (in  lateral  arm  of  U),  (b)  Deitero-spinal  (lateral  and  mesial), 


484 


THE  ORGANS 


^  b 

•°  s 

v^ 

w  S2 

>. 

<u 

a 

■M    O 

o  o 

O  rt 

d 

Pi 

J 

rt 

•*~i 

o^ 

;3 

rt 

en 

C/D 

o 

O 

■"■- 

o'o  d 

>   O 

■fe  m'S. 

tn  ^-> 

dti  2 

PI    O 

I*  s  P 

g^ 

^^ 

^^""^ 

s 

g    CU„- 

U 

'.    cn 

O  m  o 
+3  fe  C 

1) 

^o 

cS  "^ 

'S 

CO   *^ 

a  C 

Q 
Id 

^  ■'  »-. 

g--d 

oH 

g^8 

f^ 

THE   NERVOUS   SYSTEM  485 

(c)  tract  from  nucleus  of  medial  longitudinal  fasciculus  (mesial),  (d)  colliculo- 
spinal  (mesial),  (e)  shorter  descending  and  ascending  tracts  which  may  be  re- 
garded as  the  equivalent  of  the  ground  bundles  of  the  cord  comprising  shorter 
reticulo-spinal  and  spino-reticular  fibres.  The  shortest  of  these  fibers,  which  in 
the  cord  were  next  the  lateral  gray,  are  now  mingled  with  the  gray,  the  combina- 
tion constituting  the  gray  reticular  formation.  Other  short  intra-  and  interseg- 
mental tracts  lie  in  and  adjoining  the  dorsal  horn,  as  in  the  cord. 

Descending  suprasegmental  paths  include  certain  of  the  above  long  descend- 
ing intersegmental  tracts  as  previously  explained.  Besides  these  there  are  the 
eferent  suprasegmental  neurones  known  as  the  pallio-spinal  or  pyramidal  tracts 
and  the  colliculo-spinal  tracts.  Bundles  of  fibres  are  seen  crossing  {pyramidal 
decussation)  from  the  anterior  pyramid  of  one  side  to  the  opposite  dorso-lateral 
column,  where  they  turn  downward  as  the  crossed  pyramidal  tract.  In  their 
passage  through  the  gray  matter,  they  cut  off  the  ventral  horn  from  the  rest  of 
the  gray  matter.  These  fibres,  as  already  noted  in  the  cord,  are  descending 
axones  from  motor  cells  situated  in  the  precentral  cerebral  cortex.  In  the  pyram- 
idal decussation  most  of  these  fibres  cross  to  the  opposite  dorso-lateral  region 
to  pass  down  the  cord  as  the  crossed  pyramidal  tract  (p.  464,  and  Fig.  318; 
Fig.  322,  F).  The  remaining  fibres  stay  in  their  original  anterior  position  and 
continue  down  the  cord  as  the  direct  pyramidal  tract  (p.  465,  and  Fig.  318; 
Fig.  322,  F).  A  few  pass  to  the  ventral  tract  in  the  same  side,  thus  becoming 
uncrossed  fibres  in  the  lateral  tract.  The  bundles  of  fibres  do  not  cross  in  a  trans- 
verse plane,  but  take  a  downward  direction  at  the  same  time.  For  this  reason 
transverse  sections  show  these  fibres  cut  rather  obliquely.  Because  of  the  fact 
that  the  fibres  cross  in  alternate  bundles,  the  number  of  decussating  fibres  seen 
in  any  one  section  is  greater  on  one  side  than  on  the  other  (Fig.  324). 

2.  Transverse  Section  of  the  MeduUa  through  the  Decussation  of  the  Fillet 
or  Lemniscus  (Sensory  Decussation)   (Figs.  324  and  326) 

The  most  conspicuous  features  are  the  appearance  of  the  nuclei  cuneatus  and 
gracilis,  the  decussation  and  formation  of  the  medial  lemniscus  or  fillet,  and  the 
increase  of  the  gray  reticular  formation. 

Peripheral  Efferent  Neurones. — In  the  lateral  part  of  the  central  gray  is  the 
dorsal  nucleus  of  the  X  {nucleus  alee  cinerecB).  In  the  ventral  part  of  the  central 
gray  is  the  nucleus  hypoglossi  and,  passing  ventrally  and  emerging  lateral  to  the 
pyramids,  may  be  seen  the  axones  of  its  cells — the  root  fibres  of  the  XII. 

In  tht  nucleus  XII  can  be  distinguished  (Weigert  stain)  coarse  fibres  which 
arc  the  root  fibres,  and  fine  fibres  which  arc  terminals  of  other  fil)res  ending  in 
the  nucleus.  Among  these  have  been  distinguished  collaterals  from  secondary 
vagoglossopharyngeal  and  trigeminal  tracts  (three-neurone  reflex,  and  from 
various  parts  of  the  reticular  formation.  Whether  pyramidal  fibres  reach  the 
nu(l'.-iis  directly  or  via  int(T(  alntcd  neurones  is  uncertain. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — Entering 
afferent  root  fibres  are  usually  not  present. 

The  funiculi  or  fasciculi  cuneatus  and  gracilis  have  diminished,  and  internal 
to  them  have  appeared  large  masses  of  gray.     These  are  the  nuclei  of  the  columns, 


486 


THE  ORGANS 


Pi    S- 


^  S  o  ^ 

in 

mi 

F  " 

orN. 


> 

.2 

C! 

aj 

cd 

>-j 

;-i 

rf 

H 

M 

1^ 

D. 

-d 

■u 

M 

i-i 

rf)  tu 

bO 

<L> 

d 

L*" 

^ 

p4  O 


THE  NERVOUS   SYSTEM  487 

and  are  known,  respectively,  as  the  nucleus  of  the  column  of  Goll  or  the  nucleus 
gracilis,  and  the  nucleus  of  the  column  of  Burdach  or  the  nucleus  cuneatus.  In  the 
higher  sensory  decussation  levels  there  is  usually  an  accessory  cuneate  nucleus. 

These  nuclei  serve  as  nuclei  of  termination  for  the  fibres  of  the  posterior 
funiculi.  Their  termination  in  these  nuclei  is  the  ending  of  that  system  of  fibres 
which  has  been  traced  upward  from  their  origin  in  the  cells  of  the  spinal  ganglia; 
the  completion  of  the  course  of  the  spinal  peripheral  afferent  neurones.  As  the 
fibres  of  the  posterior  columns  are  constantly  terminating  in  these  nuclei,  there 
is,  in  passing  from  below  upward,  a  constant  increase  in  the  size  of  the  nuclei 
and  a  corresponding  decrease  in  the  size  of  the  posterior  columns,  until,  just  below 
the  olive,  the  whole  of  the  column  of  GoU  and  most  of  the  column  of  Burdach 
are  replaced  by  their  respective  nuclei.     (Pp.  461,  462.) 

Study  the  plexus  of  fine  fibres  in  these  nuclei,  formed  by  the  terminals  of  the 
column  fibres,  also  the  coarser  fibres  (axones  of  the  cells  of  the  nuclei)  gathered 
in  the  ventral  part  of  the  nuclei,  whence  they  emerge  and  curve^  around  the  cen- 
tral gray,  cross  to  the  opposite  side  ventral  to  it  and  dorsal  to  the  pj^ramids,  and 
then  turn  brainward  forming  the  bundle  of  fibres  known  as  the  medial  lemniscus 
or  medial  fillet. 

The  spinal  V  has  increased  and  also  its  terminal  nucleus,  the  dorsal  horn. 
The  spino-cerebellar  and  spino-thalamic  tracts  occupy  about  the  same  positions. 

In  the  centra]  gray  dorsal  to  the  central  canal  is  a  nucleus  representing  a 
union  of  the  caudal  ends  of  the  terminal  nuclei  of  the  fasciculi  solitarii  (see  next 
section) — the  nucleus  commissuralis.  Fibres  of  the  fasciculi  solitarii  also  de- 
cussate here. 

Intersegmental  Neurones. — The  rubro-spinal  and  Deitero-spinal  tracts  and 
the  tract  from  the  nucleus  of  the  medial  longitudinal  fasciculus  occupy  about  the 
same  positions.  The  reticular  formation  has  increased,  the  whole  of  the  ventral 
horn  and  intermediate  gray  containing  bundles  of  longitudinal  fibres.  The 
formation  is  also  traversed  by  transverse  fibres,  representing  the  beginnings  or 
terminations  of  various  longitudinal  fibres. 

Efferent  Suprasegmental  Neurones. — The  decussation  of  the  pyramids  has 
now  nearly  or  entirely  ceased.  The  lateral  pyramidal  tracts  are  no  longer  in  the 
lateral  columns  but  are  parts  of  the  anterior  pyramidal  tracts  which  form  two 
large  masses  of  fibres  one  on  each  side  of  the  ventral  sulcus.  The  coUiculo- 
spinal  tract  occupies  the  same  position. 

3.  Transverse  Section  of  the  Medulla  through  the  Lower  Part  of  the  Inferior 
Olivary  Nucleus  (Figs.  324  and  327) 

The  central  canal  has  opened  into  the  fourth  ventricle,  the  central  gray  (in- 
cluding the  central  gelatinous  substance)  now  being  spread  out  on  its  floor.  The 
roof  of  the  ventricle  is  formed  by  its  chorioid  plexus.  The  most  conspicuous 
new  feature  is  the  olive. 

Efferent  Peripheral  Neurones— The  nucleus  of  the  XII  is  large  and  occupies 

*  Fibres  having  a  transverse  curved  or  arched  course  are  in  general  termed  arcuate 
fibres.  If  they  are  (ieei)ly  located,  they  are  internal  arcuate  fibres,  if  near  the  j)eriphcry, 
they  are  superficial  or  external  arcuate  fibres.  Obviously  the  same  fibre  may  be,  in 
different  parts  of  its  course,  internal  arcuate,  external  arcuate,  and  longitudinal. 


488 


THE  ORGANS 


H  f^ 


THE   NERVOUS   SYSTEM 


489 


the  swelling  in  the  floor  of  the  ventricle  each  side  of  the  median  line  known  as 
the  eminentia  or  trigonum  hypoglossi.  The  root  fibres  of  the  XII  pass  lateral  to 
the  medial  lemniscus,  between  the  olive  and  pyramid,  and  then  emerge  at  the 
groove  between  olive  and  pyramid. 

The  dorsal  nucleus  of  the  X  occupies  a  sweUing  lateral  to  the  preceding  and 
known  as  the  ala  cinerea.  Some  of  the  root  fibres  of  the  X  are  axones  from  this 
nucleus.  They  probably  innervate  (via  sympathetic  neurones)  some,  at  least,  of 
the  smooth  muscles,  heart  (and 
glands  ?),  innervated  by  the  vagus 
(X).  The  dorsal  nucleus  appears 
to  be  relatively  deficient  in  termi- 
nals. What  it  does  receive  ap- 
pears to  come  from  the  secondary 
vago-glossopharyngeal  and  tri- 
geminal tracts. 

The  bodies  of  another  group 
of  peripheral  efferent  neurones 
form  the  nucleus  ambiguus,  often 
difficult  to  distinguish,  in  the 
reticular  formation.  Their  ax- 
ones pass  obliquely  dorsally  and 
mesially,  join  the  other  root  fibres 
of  the  X,  and  then  bending  ab- 
ruptly, pass  with  them  to  the 
lateral  surface  of  the  medulla. 
Some  pass  across  the  median  line 
and  [leave  by  the  root  of  the  op- 
posite side.  They  probably  in- 
nervate the  striated  muscles  of 
the  pharynx,  larynx  (and  oesoph- 
agus ?).  The  nucleus  receives 
various  terminals,  some  at  least 
appearing  to  come  from  the 
secondary  trigeminal  tracts  and 
from  the  lateral  part  of  the  retic- 
ular formation.     (Fig.  328.) 

Afferent  Peripheral  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts.^ 
Other  root  fibres  are  the  afferent  fibres  of  the  X  which  form  a  common  root  with 
the  preceding.  Sometimes  they  can  be  seen  joining  the  fasciculus  solitarius  of 
which  they  form  a  part.  Some  fibres  or  collaterals  may  enter  the  adjacent  gray 
{terminal  nucleus  of  the  X)  (see  Fig.  328). 

If  the  roots  of  the  X  do  not  show  well  in  the  section,  defer  their  study  until 
the  following  .section  where  the  IX  shows  similar  relations. 

The  spinal  Vis  partly  [lierced  anrl  partly  covered  by  transverse  fibres,  princi- 
pally olivo-cerebellar  fibres  (see  below).  Its  terminal  nucleus  is  less  conspicuous. 
Two  new  bundles  of  descending  root  fibres  have  appeared;  one  is  iho  fasciculus 
solitarius  composed  of  the  afTerent  root  fibres  of  the  X,  IX  (including  gustatory 


Fig.  328. — Diagram  of  Origin  of  Cranial 
Nerves  X  and  XII.  (Schafer.)  />jyT,  Pyramid; 
0,  olivary  nucleus;  r,  restiform  body;  d.V,  spinal 
root  of  fifth  nerve;  n.XII,  nucleus  of  hypo- 
glossal; XII,  hypoglossal  nerve;  d.n.X.XI, 
dorsal  nucleus  of  vagus;  n.amb,  nucleus  am- 
biguus;/.5.,  solitary  fasciculus  (descending  root 
of  vagus  and  glosso-pharyngeal) ;  f.s.n,  nucleus 
of  solitary  fasciculus;  X,  motor  fibre  of  vagus 
from  nucleus  ambiguus;  g,  ganglion  cell  of 
sensory  root  of  vagus  sending  central  arm  into 
solitary  fasciculus  {f.s.)  and  collateral  to  its 
nucleus  {f.s.n.);  f.s.n,  cell  of  nucleus  of  solitary 
fasciculus  sending  axone  as  internal  arcuate 
fibre  to  opposite  side  of  cord  (secondary  vagus 
and  glossopharyngeal  tract.)  This  course  of 
the  secondary  tract  is  doubtful. 


490  THE   ORGANS 

fibres),  and  higher  up,  of  the  VII.  A  small  mass  of  gray  of  a  gelatinous  appear- 
ance near  it  is  its  terminal  nucleus.  The  course  of  the  secondary  tract  cannot  be 
made  out  and  is  not  accurately  known.  The  other  bundle  is  the  descending 
vestibular  root.  It  lies  lateral  to  the  fasciculus  solitarius.  Accompanying  it  are 
cells  which  constitute  its  terminal  nucleus.  Occupying  the  floor  of  the  ventricle 
lateral  to  the  dorsal  nucleus  of  the  X  is  another  terminal  nucleus  of  the  vestibular 
nerve,  the  nucleus  medialis  (triangular  or  chief  nucleus.)  Internal  arcuate 
fibres  emerging  from  these  regions  ma}^  represent  secondary  tracts  (probably 
reflex)  from  these  nuclei.     (P.  493;  Fig.  331.) 

The  nucleus  gracilis  has  disappeared.  The  nucleus  cuneatus  may  be  pre- 
sent, much  diminished,  and  give  rise  to  some  internal  arcuate  fibres  to  the 
medial  lemniscus.  The  lemniscus  is  now  a  tract  which  has  become  built  up 
on  each  side  of  the  median  line.  This  latter  is  known  as  the  raphe  (i.e., 
"seam,"  stitched  by  the  decussating  fibres). 

The  ventral  spino-cerebellar  tract  and  spino-thalamic  tract  are  in  about  th,e 
same  lateral  position,  but  the  dorsal  spino-cerebellar  tract  has  moved  dorsally 
and  together  with  olivo-cerebellar  fibres  (see  below)  begins  to  form  the  restiform 
body  (see  below). 

In  the  lateral  part  of  the  reticular  formation,  between  spinal  V  and  olive  are 
seen  the  nuclei  laterales.  In  these  nuclei  some  of  the  spino-cerebellar  fibres  end. 
The  axones  of  these  nuclei  partly  enter  the  restiform  body  on  the  same  side  and 
partly  cross  to  the  opposite  restiform  body  (p.  507;  Fig.  337).  They  form  some 
of  the  ventral  external  arcuate  fibres  seen  in  the  section.  The  lateral  nuclei  are 
thus  partial  interruptions  in  the  spino-cerebellar  path.  The  nuclei  arcuati  are 
well  marked. 

Other  Afferent  Cerebellar  Neurones. — A  new  and  important  convoluted  mass 
of  gray  is  the  inferior  olivary  nucleus,  forming  the  bulge  of  the  lateral  surface  of 
the  medulla  known  as  the  olive.  Near  it  are  the  dorsal  and  medial  accessory 
olives.  The  axones  of  the  olivary  cells  are  the  olivo-cerebellar  fibres.  They  cross 
through  the  fillets,  pass  through  or  around  the  opposite  olivary  nucleus,  thence 
proceed  dorso-laterally,  being  gathered  into  more  compact  bundles,  traverse  or 
surround  the  spinal  V  and  dorsal  to  it  bend  longitudinally,  forming  a  great  part 
of  the  restiform  body.  The  latter  produces  an  eminence  on  the  dorso-lateral 
surface  of  the  medulla.  The  restiform  body,  thus  formed  by  these  spino-cere- 
bellar and  olivo-cerebellar  fibres,  together  with  certain  others,  passes  into  the 
cerebellum  higher  up,  forming  the  major  part  of  the  inferior  cerebellar  arm  or 
peduncle.  According  to  many  authorities  fibres  from  the  columns  and  nuclei 
of  Goll  and  Burdach  of  the  same  side  (dorsal  external  arcuate  fibres)  and  opposite 
side  (ventral  external  arcuate  fibres)  may  join  the  restiform  body.     (Comp. 

P-  507-) 

Fibres  appearing  on  the  external  surface  of  the  olivary  nucleus  are  the  term- 
ination of  a  large  tract  descending  to  the  olivary  nucleus,  the  central  tegmental 
tract.     Its  origin  in  higher  levels  is  not  accurately  known. 

Intersegmental  Neurones. — The  reticular  formation  is  now  still  more 
extensive. 

The  original  U-shaped  mass  of  intersegmental  tracts  (and  the  coUiculo-spinal 
tract)  has  now  become  widely  separated  into  two  parts.     The  lateral  part,  con- 


THE  NERVOUS   SYSTEM  491 

sisting  principally  of  the  rubro-spinal  tract  and  uncrossed  Deitero-spinal  fibres, 
lies  mesial  to,  or  partly  mingled  with,  the  spino-thalamic  and  ventral  spino-cere- 
bellar  tracts.  The  mesial  part  of  the  U,  consisting  principally  of  crossed  and 
uncrossed  Deitero-spinal  fibres  and  fibres  from  other  nuclei  in  the  reticular 
formation,  and  of  fibres  from  the  nucleus  of  the  medial  longitudinal  fasciculus, 
now  forms  the  medial  longitudinal  fasciculus  dorsal  to  the  fillet.  Near  this 
bundle,  or  united  with  it,  is  the  colliculo-spinal  tract  {predorsal  tract).  When  these 
tracts  have  passed  down  to  below  the  formation  of  the  fillet  and  the  olives,  they 
assume  the  positions  noted  in  the  lower  levels  of  the  medulla. 

Efferent  Suprasegmental  Neurones. — The  pyramids  are  the  same.  Small 
bundles  of  more  lightly  stained  fibres  present  in  the  fillet  here  and  in  higher 
levels  (Weigert  stain,  not  indicated  in  the  figures)  are  efferent  pallial  fibres 
detached  from  pes  or  pyramids.  They  are  aberrant  fibres  which  rejoin  the  pyra- 
mids or  are  fibres  innervating  motor  cranial  nuclei.  The  colliculo-spinal  tract 
(see  above). 

4.  Transverse   Section  of  the    Medulla  through  the  Middle  of   the  Olivary 

Nucleus 

Such  a  section  is  so  similar  to  3  and  5  that  its  detailed  description  may  be  omit- 
ted. The  nucleus  cuneatus  has  disappeared;  the  fillet  increased  somewhat; 
fasciculus  solitarius  and  descending  vestibular  root  have  increased;  also  their 
terminal  nuclei.  The  olivary  nucleus,  olivo^cerebellar  fibres,  and  the  restiform 
body  have  greatly  increased.     The  formatio  reticularis  has  increased  in  extent. 

5.  Transverse  Section  of  the  Medulla  through  the  Entrance  of  the  Cochlear 

Root  of  Nerve  VIII  (Figs.  324  and  329) 

Efferent  Peripheral  Neurones. — The  dorsal  vagus  nucleus  is  not  present, 
but  the  nucleus  ambiguus  is  usually  present  and  probably  sends  some  axones  to 
nerve  IX,  passing  out  with  the  afTerent  fibres  (see  below).  The  nucleus  XII 
has  disappeared  and  also  its  root  fibres. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — Usually 
the  afferent  root  fibres  of  nerve  IX  are  present.  They  enter  on  the  lateral  aspect 
of  the  medulla  ventral  to  the  restiform  body,  traverse  the  spinal  V,  and  pass  to 
the  fasciculus  solitarius  or  its  terminal  nucleus.  The  fasciculus  solitarius 
is  smaller,  and  just  above  the  entrance  of  the  IX  consists  of  only  a  comparatively 
few  descending  afferent  root  fibres  of  the  VII. 

The  fibres  of  the  cochlear  nerve  enter  the  extreme  lateral  angle  of  the  medulla, 
where  many  or,  according  to  some,  all  of  them  terminate  in  two  masses  of  cells 
enveloping  externally  the  restiform  body  and  known  as  the  ventral  (or  accessory) 
and  dorsal  (or  lateral)  cochlear  nuclei.  Most  of  the  axones  of  the  dorsal  nucleus 
pass  across  in  the  floor  of  the  ventricle  {strice  medullares)  to  form  a  part  of  the 
opposite  secondary  tract  (lateral  lemniscus)  of  the  cochlear  nerve.  The  axones 
of  the  ventral  nucleus  also  decussate,  but  by  a  more  ventral  route,  (trapezius), 
and  also  form  a  part  of  the  lateral  lemniscus.  This  latter  decussation  takes 
place  at  a  higher  level  (sec  next  section). 


492 


THE  ORGANS 


tn 

m 

U. 

Vh 

o 

> 

M 

a 

H 

1 

Pi 

M 

a 

rl' 

o 

THE   NERVOUS   SYSTEM  493 

The  auditory  nerve  is  divided  into  two  parts:  the  cochlear  nerve  (gangHon 
spirale)  and  the  vestibular  nerve  (ganghon  of  Scarpa).  The  fibres  of  the  coch- 
lear root  enter  at  a  lower  level  than  those  of  the  vestibular.  Some  of  them  enter 
the  ventral  cochlear  nucleus;  the  remainder  pass  dorsalward  to  the  dorsal 
cochlear  nucleus,  or  nucleus  of  the  acoustic  tubercle.  According  to  some  author- 
ities, some  root  fibres  pass  to  the  superior  olivary  and  trapezoid  nuclei.  The 
axones  of  the  cells  of  the  ventral  and  dorsal  nuclei  form  the  secondary  cochlear 
tract  (lateral  fillet).  These  fibres  decussate  and  send  collaterals  to,  or  are 
partially  interrupted  in,  the  nucleus  ohvaris  superior,  trapezoideus,  nucleus 
of  lateral  fillet  and  inferior  coUiculus  (posterior  corpus  quadrigeminum). 
According  to  some  authorities  all  the  fibres  of  the  lateral  lemniscus  terminate 
in  the  inferior  coUiculus.  From  the  inferior  colliculus  the  path  is  formed  by  the 
arm  or  brachium  of  the  latter  to  the  medial  geniculate  body  and  thence  to  the 
temporal  cortex  cerebri.  It  is  thus  not  possible  to  state  definitely  how  many 
neurone  systems  are  involved,  but  the  principal  ones  are:  (i)  ganglion  spirale, 
(2)  dorsal  and  ventral  nuclei  and  (decussation)  lateral  lemniscus,  (3)  posterior 
corpus  quadrigeminum  and  its  brachium,  (4)  medial  geniculate  body  of  the  thal- 
amus and  geniculo-cortical  fibres.  If  the  lateral  lemniscus  fibres  be  regarded 
as  simply  passing  by  the  posterior  corpus  quadrigeminum,  giving  collaterals  to 
it  (Cajal),  the  path  would  in  part  consist  of  three  neurone  systems  analogous 
to  those  of  the  paths  from  the  cord,  trigeminus  and  eye.     (Figs.  323,  330.) 

The  fibres  of  the  vestibular  root  enter  higher  and  mesial  to  those  of  the  coch- 
lear root,  passing  dorsally  along  the  inner  side  of  the  restiform  body  to  four 
terminal  nuclei,  which  cannot  all  be  clearly  seen  in  any  one  section;  (a)  Deiters' 
nucleus  (lateral  vestibular  nucleus)  situated  at  the  end  of  the  main  bundle  of 
root  fibres,  just  internal  to  the  restiform  body ;  {b)  von  Bechterew's  nucleus  (supe- 
rior vestibular  nucleus)  situated  somewhat  dorsal  to  Deiters'  nucleus  in  the  lateral 
wall  of  the  fourth  ventricle;  (c)  the  median  or  principal  nucleus  of  the  vestibular 
division — a  large  triangular  nucleus,  occupying  a  considerable  part  of  the  floor 
of  the  fourth  ventricle;  (d)  the  descending  vestibular  nucleus  which  accompanies 
the  descending  fibres  of  the  vestibular  root  (spinal  eighth).  Fibres  also  pass  to 
the  cerebellum.  The  axones  of  the  cells  of  the  terminal  vestibular  nuclei  form 
the  secondary  vestibular  tracts,  some  axones  going  to  (a)  the  cerebellum  (?),(b) 
the  midbrain,  especially  to  the  nuclei  of  nerves  III  and  IV  (via  Deiters  and  von 
Bechterew,  the  former  by  the  medial  longitudinal  fasciculus),  (c)  the  medulla 
and  cord,  probably  to  various  motor  nuclei,  via  the  medial  longitudinal  fasciculus, 
lateral  tract  from  Deiters'  nucleus  and  other  tracts  in  the  reticular  formation. 
(Figs.  323,  331  and  337.) 

The  descending  vestibular  root  is  large,  as  is  also  its  terminal  nucleus  and  the 
medial  terminal  vestibular  nucleus,  in  the  present  section. 

The  spinal  \'  is  unchanged,  its  terminal  nucleus  being  rather  indistinct. 
Secondary  trigeminal  tracts  cannot  be  distinguished — such  fibres  probably  either 
join  the  medial  lemniscus  or  form  an  inrlependent  ascending  tract  in  the  reticular 
formation.  'J"he  fillet  is  about  the  same.  'J'he  venlral  spino-cerebellarand  si)ino- 
ihalaniii   I  rai  ts  arc-  in  1  lie  same  posil  ions. 

Other  Afferent  Cerebellar  Neurones.  The  olives  are  still  larger  and  send 
many  bundles  of  olivo-cerebcUar  fibres  to  the  opposite  restiform  body  which  has 


494 


THE  ORGANS 


Nu.  Corf),  trabe^oidei 
:—....... OlivOL  sub^rior 


Fig.  330 


THE   NERVOUS   SYSTEM  495 


EXPLANATION  OF  FIG.  330 

Fig.  330. — ^Diagram  showing  Connections  of  the  Cochlear  Portion  of  the  Auditory 
(VIII)  Nerve.  A,  Section  at  level  of  superior  colliculi  {Ant.  cor  p.  quad.)  and  red 
nucleus;  B,  through  level  of  inferior  colliculi  {Corpus,  quad.  ^05^.);  C,  through  level  of 
nucleus  of  lateral  lemniscus  {Nii.  lem.  lat.);  D,  through  pons  at  level  of  VIII  nerve. 
Spacing  between  the  different  levels  is  not  proportionate.  In  B  and  C  the  basis 
pedunculi  is  omitted.  Each  neurone  group  is  indicated  by  one  or  several  individual 
neurones. 

Neurone  No.  i. — Cell  bodies  in  spiral  ganglion  {gang,  spiralis);  peripheral  processes 
end  in  organ  of  Corti;  central  processes  terminate  principall}'  in  ventral  or  accessory 
nucleus  {N^u.  accessorius)  and  lateral  nucleus  {Nu.  lateralis)  or  tuberculum  acusticum; 
some  also  terminate  in  superior  olives  {Oliva  superior),  and  nuclei  of  trapezoid  body  {Nu. 
Corp.  trapezoidei)  of  same  and  opposite  sides. 

Neurone  No.  2.  (and  3  ?).• — Axones  of  cells  in  accessory  nucleus,  in  superior  olives,  and 
in  nuclei  of  trapezoid  body,  constitute  a  ventral  path  in  the  lower  border  of  the  tegmen- 
tum, and  form  the  lateral  part  of  the  lateral  lemniscus  {Lemniscus  lateralis)  or  lateral 
fillet  on  the  opposite  side.  Axones  of  cells  in  the  lateral  nucleus  traverse  the  floor  of  the 
fourth  ventricle  as  the  striae  medullares,  forming  a  dorsal  pathway,  decussate  and  then 
turn  ventrally  to  a  point  dorsal  to  the  superior  oUve  and  join  the  lateral  lemniscus  as  its 
mesial  part.  Some  axones  also  of  cells  in  the  accessory  and  lateral  nuclei  pass  dorsally, 
looping  around  the  restiform  body,  and  then  proceed  ventrally  (bundle  of  Held)  to  join 
the  opposite  lemniscus.  The  lateral  lemniscus  passes  upward  to  the  inferior  colliculus, 
some  of  the  axones  terminating  en  route  in  the  nucleus  of  the  lateral  lemniscus.  From 
cells  in  this  nucleus  some  axones  again  join  the  lateral  lemniscus,  and  a  few  decussate  and 
then  pass  upward  to  the  inferior  coUiculius.  The  axones  of  the  lateral  lemniscus  ter- 
minate in  the  inferior  colliculus,  or  pass  on  to  terminate  in  the  internal  geniculate 
body,  merely  giving  off  collaterals  to  the  superior  colliculus.  Some  fibres  of  the  lateral 
lemniscus  probably  go  to  the  superior  colliculus. 

Neurone  No.  3  (and  4?). — Axones  of  cells  in  the  gray  matter  of  the  inferior  col- 
liculus form  its  brachium  {Brachium  corp.  quad,  post.)  and  ascend  to  terminate  in  the 
internal  or  medial  geniculate  body  {Corp.  genie,  inter.). 

Neurone  No.ii,  (and  5?). — Axones  of  cells  in  the  internal  geniculate  body  pass  as  a 
part  of  the  thalamic  radiation  via  the  posterior  part  of  the  internal  capsule  to  the  cortex 
of  the  temporal  lobe  of  the  cerebrum. 

The  axones  which  constitute  the  ventral  path  (Neurones  i  and  2)  form  a  bundle  of 
fibres  known  as  the  trapezoid  body  {Corpus  trapezoideum)  or  trapezius.  The  decussa- 
tion of  these  is  peculiar  in  that  the  dorsal  axones  of  the  bundle  on  one  side  become  the 
ventral  ones  on  the  opposite  side;  this  accounts  for  the  convergence  of  the  a.xones  at  the 
median  raphe. 

Axones  of  ceils  in  the  superior  olive  pass  to  the  nucleus  of  VI  nerve  (reflex).  There  is 
possibly  also  a  descending  path  from  the  lateral  nucleus  to  the  spinal  cord  (not 
indicated). 


496 


THE  ORGANS 


Corp.  guad.  ii.^§^- 
...Itet-l 


'^'t^Mr 


Fig. 


33^- 


THE   NERVOUS   SYSTEM  497 


EXPLANATION  OF  FIG.  331 

Fig.  331. — Principal  Connections  of  the  Vestibular  Portion  of  the  Auditory  (VIII) 
Nerve.  .4,  Section  at  level  of  oculomotor  (III)  nerve;  B,  section  through  pons  and  cere- 
bellum; C,  through  inferior  olives;  D,  through  spinal  cord.  Each  neurone  group  is 
indicated  by  one  or  several  individual  neurones. 

Neurone  No.  i. — Cell  bodies  in  ganglion  of  Scarpa;  peripheral  processes  end  in  semi- 
circular canals;  central  processes  bifurcate,  and  ascending  arms  go  to  Deiters'  nucleus 
(A'«.  lat.  n.  vestib.)  (i  a),  to  von  Bechterew's  nucleus  {Nu.  sup.  n.  vestib.)  (i  b),  and 
to  nuclei  fastigii  and  cortex  of  vermis  of  cerebellum  (i  c);  descenchng  arms  go  to  nucleus 
of  descending  root  {Nu.  n.  vestib.  desc.)  (i  d)  and  (collaterals?)  to  principal  or  median 
nucleus  {Nu.  med.  n.  vestib.)  (i  c). 

Neurone  No.  2. — Axones  of  some  cells  in  Deiters'  nucleus  descend  {Tr.  desc.  nu. 
Deitersi)  uncrossed  to  antero-lateral  column  of  the  cord,  axones  of  other  cells  enter  the 
posterior  longitudinal  fasciculus  (Fasc.  long,  post.,  2  b)  of  same  side  and  descend  to 
anterior  column  of  the  cord,  others  pass  to  the  medial  longitudinal  fasciculus  of  opposite 
side  whence  some  (2  c)  descend  to  anterior  column  of  the  cord,  occupying  a  position  near 
the  anterior  median  tissure,  while  some  (2  d)  ascend  in  the  medial  longitudinal  fasciculus 
and  terminate  principally  in  the  nuclei  of  VI,  IV,  and  III  nerves.  Axones  of  cells  in  von 
Bechterew's  nucleus  ascend  (2  e),  joining  lateral  part  of  medial  longitudinal  fasciculus  of 
same  side,  and  terminate  in  nuclei  of  IV  and  III  nerves.  Axones  of  cells  in  the  nucleus 
of  the  descending  root  probably  pass  in  part  to  lateral  part  of  reticular  formation  of  same 
and  opposite  sides,  ascending  and  descending  (to  other  motor  nuclei?).  Axones  of  cells 
in  the  median  nucleus  probably  pass  largely  into  the  reticular  formation,  possibly  also  to 
the  medial  longitudinal  fasciculus  (not  indicated).  Axones  of  cells  in  the  nuclei  fastigii 
of  the  cerebellum  pass  to  von  Bechterew's  nucleus  (2/)  and  to  Deiters'  nucleus  (2  g).  The 
cerebellar  associations  intercalated  between  these  (2/,  2  g)  and  the  vestibular  fibres  to 
the  cerebellum  (i  c)  are  not  known.  (It  is  evident  that  impulses  other  than  vestibular 
ones  entering  the  cerebellum  mcjy  also  by  2 /and  2g  act  indirectly  upon  the  motor  nuclei 
innervated  by  axones  of  the  cells  in  Deiters'  and  von  Bechterew's  nuclei.  Compare 
Figs.  323  and' 337.) 


498 


THE  ORGANS 


md'  /f- 


Nvm 


sra 


-"-Fa 

vin 


"'/   NVII 


Fig  ^^2— Section  through  the  Hindbrain  at  the  Level  of  the  Junction  of  Ponsand 
Cerebdlum  ;nd  the  Entrance  of  the  Vestibular,  Part  of  the  Eighth  ferve.  Weigert 
nrenaration  (Marburg.)  Va,  Radix  spinalis  tngemini  (spmal  root  of  the  tittJij,  V i, 
Servus  abducins  (external  eye'  muscle  nerve);  y//a,  pars  nuclearis  nervi  facialis  (pars 
Srima  crus  of  origin  or  ascending  facial  root);  VIII,  nervus  acusticus  (eighth,  vestibular 
S;'  TA/brachium  pontis  (middle  cerebellar  peduncle) ;  5rcibrachium  conjunc  ivum 
[superior  cerebellar  peduncle) ;  cH,  fasciculus  tegmenti  centralis;  Q&,  .^TJlTe  £.'" 
fEssickVCrs^  corpus  restiforme;  Dca,  decussatio  cerebelh  anterior;  I^ec/  declive,  J^mb, 
SSu  '(nucleus  e'^bohformis);/.  P.   fibr.  p^ 

bulbaris    uncinate  bundle  of  Russell);//.^,    pedunculus  Ao^^-^^' /^^.^' ,f  ^^^^f  °^°  ^"^ 
Lm,    Lemniscus    medialis   (mesial  fillet  tract);  NVII,  nucleus    facialis   ^^^^^^J^''^^^ 
of  facial  nerve);  NaB,   nucleus  angularis,  or  superior,  vestibularis  (Bechterew),  Ndt 
Slleus    dentatus    cerebelli;    Nod,   Ldulus    cerebeUi;    iV..    nucleus    oh^^ns  supenor 
Nrl,    nucleus    reticularis    lateralis    (nucleus    of    the     ^toal    column)      iVrt^,m^^^^^^^^^^ 
reticularis    te-menti;  Nt,    nucleus    tecti   (nucleus    fastigu);    iVz-w,    nucleus  vestibularis 
rJaSoceTlularis  or  lateralis  (Deiters)   (large-celled  nucleus  of  vestibular  nerve);    PlcU 
plSuschSeus  lateralis;  P.,  pons;pi  pyramid ; S^nstraturn  -termedium   pedun^^^^^^^^^^^^ 
Tr,  corpus  trapezoides;   vIV,  ventriculus    quartus;  vNdt,  vellus  nuclei  dentati  cerebellx 
(fleece  of  the  cerebellar  olive)- 


THE  NERVOUS   SYSTEM  499 

still  further  increased  in  size.  External  arcuate  fibres  may  be  present  and  prob- 
ably contain  fibres  to  the  restiform  body  and  possibly  fibres  from  the  cerebellum, 
which  end  in  the  reticular  formation.  The  arcuate  nuclei  are  present.  The 
central  tegmental  tract  is  larger. 

Intersegmental  Neurones. — The  reticular  formation  is  very  extended.  Its 
composition  (longitudinal  and  transverse  fibres,  and  cells)  should  be  examined 
carefuUy.  The  rubro-spinal  tract  is  in  the  same  position,  but  the  lateral  Deitero- 
spinal  tract  is  now  more  internally  located.  Its  fibres  cannot  usually  be  dis- 
tinguished, but  are  bending  inward  and  toward  its  nucleus  of  origin  (lo- 
cated somewhat  higher).  The  medial  longitudinal  fasciculus  may  be  partially 
separated  from  the  medial  lemniscus.  It  is  a  complex  bundle  and  contains  at  va- 
rious levels  (a)  descending  and  ascending  fibres  from  Deiters'  nucleus  and  other 
cells  scattered  in  the  reticular  formation,  (b)  descending  fibres  from  the  nucleus 
of  the  medial  longitudinal  fasciculus  in  the  tegmentum  of  the  midbrain.  The 
fibres  of  this  fasciculus  probably  terminate  in  many  nuclei,  especially  those  of 
eye-muscle  nerves  (III,  IV  and  VI)  (comp.  Figs.  331,  337  and  350). 

Efferent  Suprasegmental  Neurones, — The  pyramids  and  coUiculo-spinal 
tracts  are  in  the  same  positions.  The  aberrant  efferent  pallial  fibres  already 
noted  (p.  491)  may  be  seen  in  the  lemniscus. 

6.  Section  through  the  Hindbrain  at  Level  of  Junction  of  Pons  and  Cerebellum 
and  Entrance  of  Vestibular  Nerve  (Figs.  324  and  332) 

The  most  conspicuous  features  are  the  nuclei  and  fibres  of  the  pons,  added 
ventrally  to  the  preceding  structures,  which  are  now  collectively  known  as  the 
tegmentum;  the  cerebellum,  enclosing  dorsally  the  fourth  ventricle;  and  the  connec- 
tions {inferior  and  middle  peduncles,  arms,  or  brachia)  of  the  cerebellum  with  the 
rest  of  the  brain.  The  greater  part  (rtstiform  body)  of  the  inferior  peduncle 
represents  ascending  cerebellar  connections  from  all  parts  below  this  level,  the 
middle  peduncle  (from  the  pons)  is  the  second  link  in  the  descending  connection 
from  the  pallium  to  the  cerebellum  (pallio-cerebellar  path).  The  superior  ped- 
uncle (efiferent  cerebellar)  is  not  fully  formed  at  this  level.     (Comp.  p.  508.) 

Efferent  Peripheral  Neurones. — In  this  level  and  that  of  the  next  section  are 
present  the  nuclei  and  root  fibres  of  nerves  VII  and  VI. 

The  nucleus  of  nerve  VII,  or  nucleus  facialis  is  seen  occupying  a  lateral  posi- 
tion in  the  reticular  formation  similar  to  that  of  the  nucleus  ambiguus.  In  it 
may  be  made  out  the  usual  plexus  of  fine  terminals  and  the  coarser  root  fibres 
which  proceed  dorso-mesially  to  the  floor  of  the  ventricle,  where  they  partially 
envelop  the  nucleus  of  the  VI  (usually  not  present  in  this  level).  They  then 
turn  cephalad,  forming  a  compact  longitudinal  bundle  (next  section)  and  finally 
turn  vcntro-laterally  and  caudally  to  emerge  on  the  lateral  aspect  at  the  caudal 
border  of  the  pons.  This  latter  part  is  the  second  part  as  distinguished  from 
the  first  part  of  the  connection.  The  bend  is  known  as  the  genu  facialis.  Ac- 
cording to  some  authorities,  some  of  the  fibres  cross  and  pass  out  in  the  root  of 
the  opposite  side. 

Four  groups  of  cells  composing  the  nucleus  facialis  have  been  distinguished: 
three  ventral  groups  which,  jiassing  from  the  most  mesial  to  the  most  lateral 
group,  innervate  respectively  the  mu.sclcs  of  tympanum,  of  pinna  and  of  mouth 


500 


THE  ORGANS 


ventr  /i^ 


and  face.  The  dorsal  group  (to  superior  branch  of  facial)  innervates  the  frontalis, 
corrugator  supercilii  and  orbicularis  palpebrarum.  Among  the  terminals  in  the 
nucleus  have  been  distinguished  collaterals  (reflex)  from  the  lateral  part  of  the 
reticidar  formation,  from  the  secondary  acoustic  and  trigeminal  tracts  and  other 
adjacent  fibres;  also  terminals  of  the  colliculo-spinal  tract.  Whether  the  nucleus 
receives  direct  terminals  from  the  pyramids  or  whether  fibres  of  the  latter 
are  only  connected  with  it  via  intercalated  neurones  is  uncertain. 

Some  of  the  root  fibres  of  the  VI 
are  usually  seen  in  the  ventral  border 
of  the  tegmentum.  For  nucleus  see 
next  section. 

Afferent  Roots,  their  Terminal 
Nuclei  and  Secondary  Tracts. — The 
afferent  vestibular  root  fibres  enter  at 
the  caudal  border  of  the  pons  and  pass 
lateral  to  the  spinal  V,  mesial  to  the 
ventral  cochlear  nucleus  and  restiform 
body,  and  enter  the  field  previously 
occupied  by  the  descending  vestibular 
root,  the  fibres  of  which  are  a  continua- 
tion of  the  root.  Scattered  large  cells 
in  this  region  form  the  nucleus  of 
Deiters.  Dorso-mesial  to  this  is  still 
the  medial  vestibular  terminal  nucleus 
and  dorsal  to  Deiters'  at  the  external 
angle  of  the  fourth  ventricle  is  the 
superior  vestibular  terminal  nucleus  (von 
Bechterew).  Fibres  seen  passing  from 
the  vestibular  region  to  the  cerebellum 
and  lying  near  the  ventricle  are  partly 
vestibular  root  fibres  to  the  cerebellum 
(especially  to  the  nucleus  tecti,  or 
fastigii,  see  below),  and  partly  descend- 


^///t 


Fig.  333. — Diagram  of  Origin  of  Sixth 
and  Seventh  Cranial  Nerves.  (Schafer.) 
pyr,  Pyramid;  cr,  restiform  body;  dV , 
spinal  root  of  fifth  nerve;  Venlr.  IV,  fourth 
ventricle;  VIII. v,  vestibular  root  of  eighth 
nerve;  w.F/,  chief  nucleus  of  sixth  nerve; 
n'VI ,  accessory  nucleus  of  sixth  nerve;  F/, 
sixth  nerve;  n.VII,  nucleus  of  seventh 
nerve,  from  which  the  axones  pass  dorso- 
mesially  to  the  floor  of  the  ventricle,  where 
they  turn  brainward,  appearing  as  a  bundle 
of  transversely  cut  filsres,  aVII ,  and  ascend 
to  the  "genu."  g,  where  they  turn  and  pass 
ventro-laterally  and  somewhat  caudally  to 
the  surface  as  the  seventh  nerve,  VII. 

ing     fibres     from     cerebellar     nuclei 

(especially  from  the  nuclei  fastigii,  forming  fasti gio-bulbar  fibres)  to  Deiters' 
nucleus,  other  vestibular  nuclei,  and  other  cells  in  the  reticular  formation.  It 
is  thus  evident  that  such  nuclei  as  Deiters'  may  act  as  parts  of  vestibular 
bulbo-spinal  reflex  arcs  and  also  as  parts  of  efferent  and  possibly  afferent 
cerebellar  paths.  Internal  arcuate  fibres  from  the  vestibular  area  are  probably 
principally  fibres  (secondary  tracts)  from  the  various  vestibular  nuclei  to  the 
medial  longitudinal  fasciculus  and  other  tracts  in  the  reticular  formation. 
(Comp.  pp.  493,  SOI,  507,  Figs.  331,  337.) 

The  nucleus  olivaris  superior  lies  ventral  to  the  nucleus  facialis  and  lateral 
to  the  central  tegmental  tract.  This  nucleus  together  with  several  other  small 
nuclei  in  its  immediate  vicinity  (preolivary  nucleus,  semilunar  nucleus,  trapezoid 
nucleus)  is  one  of  the  nuclei  intercalated  in  the  cochlear  path  (Fig.  330)  which 
provides  reflex  connections  {e.g.,  with  the  \T  and  VII  motor  nuclei).     Lateral 


THE   NERVOUS   SYSTEIM  501 

to  it  is  seen  a  mass  of  fibres  which  pass  by  it  toward  the  median  line  through  the 
medial  lemniscus,  and  decussate,  finally  turning  longitudinally  dorso-lateral  to 
the  opposite  superior  olive.  These  are  fibres  of  the  trapezius,  and  together  with 
the  more  dorsal  secondary  cochlear  fibres  (p.  493)  form  the  lateral  lemniscus 
(See  Fig.  330  and  page  493).  The  lateral  lemniscus  is  thus  one  of  the  links  in 
the  cochlear  or  auditory  pathway.  Fibres  pass  from  superior  olive  to  nucleus  of 
nerve  VI  (reflex).  In  some  cases  the  slender  afferent  root  of  VII  {portio  inter- 
media or  nerve  of  Wrisberg)  from  the  ganglion  geniculi  may  be  seen  entering 
between  the  vestibular  and  main  facial  roots.  Its  fibres  proceed  to  a  gray  mass 
which  may  be  regarded  as  a  continuation  of  the  nucleus  fasciculi  solitarii  and  there 
probably  partly  terminate  and  partly  send  descending  arms  to  join  the  fasciculus 
solitarius. 

The  spinal  V  occupies  the  same  position  though  separated  from  the  surface 
by  the  pontile  fibres;  internal  to  it  is  its  terminal  nucleus.  Note  the  change 
in  the  shape  of  the  lemniscus.  The  ventral  spino-cerebellar  and  spino-thalamic 
tracts  are  in  the  same  position  though  herv  separated  from  the  surface  by  the 
added  pontile  fibres. 

Other  Afferent  Cerebellar  Nexxrones. — The  inferior  olives  are  not  present, 
and  the  olivo-cerebellar  fibres  are  here  entering  the  cerebellum  as  a  part  of  the 
restiform  body.  The  central  tegmental  tract  (to  the  olives)  occupies  the  ventral 
part  of  the  reticular  formation.  The  restiform  body  is  entering  the  white  matter 
of  the  cerebellum.  It  has  been  seen  to  be  composed  of  the  dorsal  spino-cerebellar 
tract,  olivo-cerebellar  fibres  and  fibres  from  the  lateral  and  possibly  other  nuclei 
in  the  reticular  formation.  The  dorsal  spino-cerebellar  tract  terminates  in  the 
cortex  of  the  vermis  or  middle  lobe  of  the  cerebellum,  the  olivo-cerebellar  fibres 
terminate  in  all  parts  of  the  cerebellar  cortex.  The  fibres  mesial  to  the  restiform 
body,  consisting  of  ascending  vestibular  fibres  to  the  cerebellum  and  descending 
fibres  to  vestibular  and  other  nuclei  (see  cerebellum) ,  are  sometimes  called  the  in- 
ternal or  jiixta-restiform  body.  This  and  the  restiform  body  proper  constitute  the 
inferior  cerebellar  peduncle.  The  pons  consists  of  gray  matter— the  pontile  nuclei 
— and  of  transverse  a.nd,longitudinal  fibres.  The  longitudinal  fibres  include  the 
pyramids  which  pass  through  to  the  medulla  and  cord,  and  other  fibres  from  the 
pallium  (pallio-pontile  or  cerebro-pontile)  which  terminate  in  the  pontile  nuclei. 
The  axones  of  the  latter  form  the  transverse  pontile  fibres  (ponto-ccrebellar 
fibres)  which  cross  and  pass  to  the  cortex  of  the  opposite  cerebellar  hemisphere. 
They  constitute  the  middle  cerebellar  peduncle  or  brachium  pontis.  (Comp. 
p.  508.) 

The  pallio-pontile  and  ponto-ccrebellar  neurones  constitute  the  pallio-ponto- 
cerebellar  path  connecting  one  cerebral  with  the  opposite  cerebellar  hemisphere 
(p.  477,  path  XllI).  There  are  probably  also  transverse  fibres  in  the  pons 
connecting  cerebellum  and  reticular  formation.  Fibres  passing  vertically  in 
the  raphe  from  pons  to  reticular  formation  [perpendicular  fibres  of  pons)  may  be 
in  part  continuations  of  these  and  in  ijart  efferent  pallial  fibres  from  pes  to  teg- 
mentum. The  latter  arc  cither  aberrant  fibres  or  fibres  innervating  directly 
or  indirectly  motor  cranial  nuclei. 

Intersegmental  Neurones.  -The  reticular  formation  is  extensive.  In  it 
there  may  be  distinguished,  besides  the  nuclei  already  mentioned,  various  mc^re 


502  THE  ORGANS 

or  less  well-defined  reticular  nuclei  (see  Fig.  332).  The  fibres  of  the  lateral 
Deitero-spinal  tract  (not  distinguishable)  are  here  emerging  from  Deiters' 
nucleus.  The  medial  longitudinal  fasciculus  occupies  the  same  position,  but  is 
here  well  separated  from  the  fillet.  Some  of  the  internal  arcuate  fibres  in  the 
dorsal  part  of  the  reticular  formation  may  be  fibers  from  Deiters'  nucleus  to 
the  medial  longitudinal  fasciculus.  They  may  be  crossed  or  uncrossed,  and  may 
descend  in  it  as  already  mentioned  (pp.  466  and  499,.  or  ascend  (see  Fig.  331). 
Other  internal  arcuate  fibres  here,  as  elsewhere,  pass  from  the  various  terminal 
nuclei  to  form  secondary  tracts.  Other  transverse  fibres  are  axones  of  cells  of 
reticular  nuclei  or  collaterals  and  terminals  ending  in  them. 

Efferent  Suprasegmental  Neurones. — The  colliculo-spinal  tract  lies  ventral 
to  the  medial  longitudinal  fasciculus.  The  pyramids  are  in  the  same  position, 
but  are  partly  surrounded  by  pontile  fibres  and  nuclei.     (See  also  pons,  above.) 

The  Cerebellum. — The  gray  matter  consists  of  the  external  gray  or  cortex, 
and  internal  nuclei  forming  interruptions  or  relays  in  paths  from  the  cortex. 
The  white  matter  consists  of  the  fibres  of  various  afferent  and  efferent  cerebellar 
paths  and  possibly  association  fibres  of  the  cerebellum.  The  cortex  is  studied 
elsewhere.  The  internal  nuclei  can  usually  be  distinguished.  They  are  the 
nucleus  dentatus  cerebelli  {corpus  dentatum),  a  convoluted  mass  of  gray  resembling 
the  inferior  olives  (and  sometimes  called  the  cerebellar  olives),  and  mesial  to 
this  the  nucleus  glohosus.  nucleus  emboliformis  and  the  nucleus  tecti  or  fastigii. 
The  nucleus  fastigii  receives  fibres  from  various  parts  of  the  cerebellar  cortex  and 
also  vestibular  root  fibres  (p.  497).  Its  axones,  in  part  at  least,  pass  to  Deiters' 
nucleus  and  other  nuclei  in  the  reticular  formation  {fastigio-bulbar  tract).  This 
forms  a  link  of  the  cortico-fastigio-Deitero-spinal  path  (p.  478,  XVIII).  The 
nucleus  dentatus,  nucleus  globosus,  and  nucleus  emboliformis  also  receive  fibres 
from  the  cerebellar  cortex.  Their  axones  form  the  superior  cerebellar  peduncle 
{bruchium  conjunctivum),  cross  and  pass  to  the  red  nucleus,  reticular  formation, 
nucleus  of  nerve  III,  and  thalamus.  At  the  level  of  the  section  the  superior  pe- 
duncle is  not  yet  fully  formed.  This  forms  links  in  both  the  cortico-dentato-rubro- 
spinal  and  the  cerebello-pallial  paths  (p.  478,  XVII  and  VII.     See  also  p.  507.) 

Note  where  possible  the  structure  of  the  plexus  chorioideus  of  the  fourth 
ventricle.  It  consists  of  a  layer  of  cuboidal  epithelial  cells  next  the  ventricle 
which  are  ectodermic,  and  an  outer  mesodermic  part  consisting  of  connective 
tissue  and  blood-vessels. 

7.  Transverse  Section  of  the  Hindbrain  through  the  Roots  of  Nerves  VI  (Ab- 
ducens  and  VII  (Facial)   (Figs.  324  and  334) 

Efferent  Peripheral  Neurones. — The  nucleus  facialis  is  usually  not  present, 
but  various  portions  of  the  root  fibres  may  be  present  (see  preceding  section), 
especially  the  longitudinal  part. 

The  nucleus  of  the  VI  or  nucleus  abducentis  is  present  in  about  the  middle  of 
the  floor  of  the  ventricle  and  just  beneath  the  central  gray  or  partly  within  it. 
Its  fibres,  the  root  fibres  of  the  abducens,  are  seen  passing  ventrally.  The  nucleus 
receives  collaterals  from  the  axones  of  Deiters'  nucleus  (secondary  vestibular) 
on  the  same  and  opposite  sides  and  collaterals  or  terminals  from  the  superior 


THE   NERVOUS   SYSTEM 


503 


L\^- 

J 

'-'V; 

a  3 

2 

iv     >     c 

c 

m  u 

.s-a 

rV    -■  s. 

V 

S  3 

c  c 

'^ 

'  ^  .  <«  > 

o 

i--a 

c  u 

c 

CX   . 

,-S-° 

o 

alis 
brospi 
spinot 
erebell 

C 

E 

o 
o 

Pi 

a 
1 

•-3     •  U 

0) 

XI 

'A 

o 

ecun 

cis  n 
Tra 

SC.  S] 

G 

H 

M:s          tt 

fn    ^ 

(^ 

504  THE  ORGANS 

olive  (secondary  cochlear).  The  exact  mode  of  connection  with  the  pyramids 
is  not  well  known. 

Afferent  Roots,  Their  Terminal  Nuclei  and  Secondary  Tracts. — The  lateral 
(Deiters')  and  medial  vestibular  nuclei  are  usually  still  present,  also  possibly  fas- 
tigio-bulbar  iibres.  The  ventral  cochlear  nucleus  has  disappeared,  but  other 
cochlear  nuclei  (superior  olivary  and  trapezoid)  are  usually  present.  Often 
fibres  can  be  seen  passing  from  the  superior  olive  to  the  nucleus  VI. 

Fibres  of  the  secondary  cochlear  tract  (corpus  trapezoideum)  are  still  traversing 
the  medial  lemniscus,  and  decussating.  The  tract  they  are  forming  (lateral 
lemniscus)  is  not  yet  very  distinct. 

The  spinal  V  is  in  the  same  position,  but  it  and  its  terminal  nucleus  tend  to 
separate  into  groups  of  fibres  and  cells,  and  to  change  their  relative  positions. 
The  medial  lemniscus  is  more  flattened  in  cross  section,  extending  transversely 
instead  of  dor so-ventr ally.  The  ventral  spino-cerebellar  tract  and  spino- 
thalamic tract  are  in  the  same  positions  in  the  external  part  of  the  tegmentum 
ventral  to  the  spinal  V  and  external  to  the  superior  olive. 

Other  Afferent  Cerebellar  Connections. — The  restiform  body  has  now 
merged  with  the  white  matter  of  the  cerebellum.  The  nuclei  and  transverse 
fibres  of  the  pons  (ponto-cerebellar  neurones)  have  increased.  The  longitudinal 
fibres  in  the  pons  at  this  level  are  principally  the  pyramids,  but  some  are  pallio- 
pontile  fibres  which  terminate  in  the  nuclei  pontis.  Perpendicular  fibres  are 
present. 

Intersegmental  Neurones. — The  reticular  formation  is  practically  unchanged. 
One  of  its  nuclei  {nucleus  reticularis  tegmenti)  'ca.n  be  seen  as  a  lighter  area 
(Weigert)  in  the  medial  part,  dorsal  to  the  medial  lemniscus.  The  rubro-spinal 
tract  is  in  the  same  position  near  or  mingled  with  the  spino-thalamic  and  ventral 
spino-cerebellar  tracts.  These  fibres  are  not  easily  distinguished  among  the 
various  fibres  of  the  cochlear  tract  which  cross  them.  The  medial  longitudinal 
fasciculus  is  now  a  well-marked  tract  occupying  the  same  position.  From  now 
on,  it  contains  ascending  fibres  from  Deiters'  nucleus  and  perhaps  other  reticular 
nuclei  besides  the  descending  fibres  from  the  nucleus  of  the  medial  longitudinal 
fasciculus. 

Efferent  Suprasegmental  Neurones. — ^The  pyramids  and  coUiculo-spinal 
tract  (predorsal  fasciculus)  occupy  the  same  positions.  The  fastigio-bulbar 
fibres  have  been  mentioned.  The  superior  cerebellar  peduncle  is  now  more 
distinct  as  it  is  being  formed  by  fibres  from  the  dentate  nucleus.  It  lies  near  the 
dorso-lateral  part  of  the  ventricle. 

8.  Transverse  Section  of  the  Hindbrain  Through  the  Roots  of  Nerve  V  (Trigem- 
inus) (Figs.  324  and  335) 

Efferent  Perip'  eral  Neurones. — Motor  nucleus  of  V.  This  is  mesial  to  the 
terminal  nucleus  of  the  V  and  its  coarse  efferent  root  fibres  may  be  seen,  in  favor- 
able levels,  passing  out  just  internal  and  somewhat  cephalad  to  the  entering 
afferent  fibres.  It  is  probable  some  of  the  fibres  cross  and  pass  out  in  the 
opposite  motor  root.  Some  of  the  finer  terminal  fibres  present  in  the  nucleus 
are  afferent  root  fibres  of  the  V  (two-neurone  arc)  and  collaterals  of  secondary 


THE   NERVOUS   SYSTEM 


505 


506 


THE  ORGANS 


tracts  of  V  (three-neurone  arc).  The  nature  of  its  connections  with  efferent 
pallial  fibres  is  not  known.  Many  collaterals  are  also  received  from  the 
mesencephalic  root.     (Fig.  336.) 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — The  afferent 
fibres  of  the  V  pass  through  the  pons  and  enter  the  tegmentum  where  they 
divide  into  short  ascending  and  long  descending  arms.  The  former,  together 
with  collaterals,  terminate  in  the  cephalic  end  of  the  terminal  nucleus  of  the  V. 
This  is  broken  up  into  groups  of  cells  which  lie  dorso-lateral  to  the  entering 
fibres  and  is  sometimes  known  as  the  "principal  sensory"  nucleus  of  the  V. 
The  long  descending  arms  pass  down  to  the  cord  as  the  spinal  V,  giving  off  collat- 
erals  and   terminals  to  the  nucleus  en  route.      (Fig.  336.)     A  third  source  of 


Fig.  336. — Diagram  of  Origin  of  Fifth  Cranial  Nerve.  (Schafer.)  .  G,  Gasserian 
ganglion;  a,  b,  c,  the  three  divisions  of  the  nerve;  m.n.V,  principal  motor  nucleus;  p.s.n.V, 
principal  terminal  "sensory"  nucleus;  d.s.n.V,  terminal  nucleus  of  spinal  root;  d.s.V, 
descending  or  spinal  root;  c.V  and  c'.V,  secondary  trigeminal  tracts  (axones  of  cells  in 
terminal  nuclei);  r,  median  raphe;  m'.n.V,  mesencephalic  nucleus. 


fibres  of  the  V  is  a  series  of  cells  extending  upward  into  the  roof  of  the  mesen- 
cephalon. The  axones  of  these  cells  form  the  mesencephalic  root  of  the  V.  There 
is  reason  to  suppose,  from  their  peculiar  location  and  for  other  reasons,  that 
these  are  afferent  peripheral  neurones  which  have  remained  within  the  neural 
tube.  From  the  region  of  the  terminal  nucleus  of  the  V,  a  transverse  bundle 
passes  to  the  opposite  side  in  the  floor  of  the  fourth  ventricle.  This  is  considered 
a  secondary  decussating  trigeminal  tract  which  forms  an  ascending  tract  in  the 
dorsal  part  of  the  reticular  formation.  Fibres  of  secondary  tracts  give  off 
collaterals  to  various  efferent  nuclei  and  probably  axones  of  some  cells  of  the 
terminal  nuclei  become  intersegmental  fibres  in  the  reticular  formation.     Second- 


2  "5 

O  o  , 

o  S 

(/)  c 


rt    o  _ 

r-    "  1 


—    J)    U    u 

3  —    ts£)  O    O 

"  o  c  c  o 


u-;^ 


.2^ 

.2     N 
•"     C     w 

«  fc  1 

o  c^ 


[l<    (O 


•s=j||.g|u   Ill's-     a;    |jj-|SQ|o^^||a  a^^g-S-i 
III  sails   m^ilf 


iiiislrs    i¥l-g-°srs=    h^kl 


i  g  "  a  a  .  a  ° 


THE   NERVOUS   SYSTEM  507 

ary  tracts  to  the  thalamus  (via  fillet  and  also  in  reticular  formation?)  form  part 
of  the  trigeminal  afTerent  pallial  path. 

The  superior  terminal  vestibular  nucleus  (of  von  Bechterew)  may  still  be 
present.  The  superior  olivary  and  trapezoid  nuclei  may  be  present.  The 
secondary  (and  tertiary  (?),  see  Fig.  330)  cochlear  tract  or  lateral  lemniscus  is 
now  well  formed  and  may  be  seen  lying  dorso-lateral  to  the  superior  olivary  and 
trapezoid  nuclei. 

The  medial  lemniscus  is  still  more  flattened.  The  spino-thalamic  and  ventral 
spino-cerebellar  tracts  occupy  the  same  positions. 

Other  Afferent  Cerebellar  Neurones. — The  transverse  pons  fibres  are  the 
same,  but  the  longitudinal  fibres  have  increased  owing  to  the  presence  of  more 
pallio-pontile  fibres.  The  perpendicular  pontile  fibres  are  seen  passing  dorsally  in 
the  raphe  into  the  tegmentum. 

The  central  tegmental  tract  is  in  nearly  the  same  position. 

Intersegmental  Neurones. — The  reticular  formation  is  somewhat  diminished. 
In  it  is  the  nucleus  reticularis  tegmenti.  The  rubro-spinal  tract  is  in  the  same 
position,  mingled  with  the  spino-thalamic  and  ventral  spino-cerebellar  tracts. 
The  medial  longitudinal  fasciculus  is  unchanged. 

Efferent  Suprasegmental  Neurones. — The  pyramids  now  occupy  the  cen- 
tral part  of  the  pons,  and  are  broken  up  into  a  number  of  bundles.  In  the 
dcrsal  part  of  the  pons  fibres  pass  obliquely  dorsally.  These  are  probably 
efferent  pallial  fibres  which  act  directly  or  indirectly  on  some  of  the  efferent 
nuclei  of  cranial  nerves  (motor  path  to  cranial  nerves).  The  pallio-pontile 
fibres  have  been  mentioned. 

The  superior  peduncle  is  now  a  large  bundle  of  fibres  flattened  against  the 
ventricular  surface  of  the  dorso-lateral  brain  wall. 

The  coUiculo-spinal  tract  is  in  the  same  position. 


Cerebellum 

The  cerebellum,  connected  with  the  rest  of  the  brain  by  its  three 
peduncles,  consists  of  two  lateral  lobes  or  hemispheres  connected  by  a 
median  lobe,  the  vermis.  These  are  divided  into  various  lobules,  the 
surfaces  of  which  are  marked  by  parallel  transverse- folds  or  laminae. 
When  these  are  cut  across  it  is  seen  that  they  give  off  secondary 
or  tertiary  laminae,  the  whole  producing  the  appearance  known  as  the 
arbor  vitse.  The  surface  of  the  cerebellum  is  composed  of  gray  matter, 
the  cortex,  enveloping  the  white  matter.  Besides  this  there  are 
masses  of  gray  within,  the  internal  nuclei  of  the  cerebellum  (dentatus, 
globosus  emboliformis,  and  fastigii),  embedded  in  its  white  matter. 
Fibres  entering  the  cortex  are  the  terminations  of  the  fibres  of  the 
restiform  body  (dorsal  spino-cerebellar  tract  to  the  cortex  of  the  vermis, 
olivo-cerebellar  fibres  to  the  whole  cortex,  fibres  from  the  lateral 
nucleus  and  possibly  other  nuclei  in  the  reticular  formation,  also  per- 


508 


THE  ORGANS 


haps  some  fibres  from  the  columns  and  nuclei  of  Goll  and  Burdach  of 
the  same  and  opposite  sides),  vestibular  root  fibres  to  the  vermis,  the 
ventral  spino-cerebellar  tract  to  the  vermis,  and  the  pontile  fibres  to 
the  cortex  of  the  hemispheres.  The  cortical  cells  do  not  send  axones 
outside  the  cerebellum,  all  efferent  fibres  being  interrupted  in  the 
internal  nuclei.  The  dentate  nucleus  receives  fibres  from  the  cortex 
of  the  hemispheres;  the  globose  and  emboliform  nuclei  receive  fibres 
from  the  cortex  of  the  vermis;  and  the  nucleus  fastigii  receives  fibres 
from  various  parts.     The  axones  of  the  first  three  form  the  superior 


Fig.  338. — Part  of  a  Vertical  Section  through  the  Adult  Human  Cerebellar  Cortex. 
Nissl  Method.  (Cajal.)  A,  Inner  portion  of  the  molecular  layer;  B,  granular  layer;  C, 
body  of  a  Purkinje  cell;  a,  stellate  cell  of  the  molecular  layer;  h,  nuclei  of  the  epithelial- 
like  neurogha  cells  (cells  of  the  fibres  of  Bergmann);  c,  stellate  cell  with  marginal  chromo- 
philic  substance;  d,  fibrillar  mass  corresponding  to  the  baskets;  e,  nuclei  of  the  granule 
cells;  /,  islands  or  glomeruli  in  the  granular  layer;  g,/z,  Golgi  cells  in  the  granular  layer; 
?',  nuclei  of  neuroglia  cells. 


peduncle;  the  axones  of  the  nucleus  fastigii  are  fastigio-bulbar  fibres, 
principally  crossed,  to  vestibular  nuclei  and  possibly  other  reticular 
formation  nuclei.  There  may  be  some  efferent  fibres  in  the  middle 
peduncle  to  reticular  formation  nuclei,  but  the  major  part,  at  least, 
of  this  peduncle  consists  of  the  ponto-cerebellar  fibres  already  de- 
scribed. The  inferior  and  middle  peduncles  are  thus  largely 
afferent  and  the  superior  peduncle  is  efferent,  to  red  nucleus,  thal- 
amus and  nucleus  of  nerve  III.  (Fig.  323,  p.  546  and  Fig.  337.) 
See  also  pp.  475  and  476. 


THE   NERVOUS   SYSTEM 


509 


In  the  cortex  can  be  distinguished  an  outer  or  molecular  layer  with 
few  cells  and  few  medullated  fibres,  an  inner,  granular  or  nuclear 
layer,  and  between  the  two  a  single  row  of  large  flask-shaped  cells, 
the  cells  o]  Purkinje  (Figs.  338,  339).  These  latter  give  off  several 
main  dendrites,  which  enter  the  molecular  layer  and  form  a  remarkably 
rich  arborization  extending  to  the  surface.  The  Golgi  method  shows 
the  larger  and  medium  branches  smooth,  but  the  terminal  branches 
thickly  beset  w4th  "gemmules."  The  dendritic  arborization  is 
flattened,  extending   at  right  angles  to  the  laminae.     The  axone  is 


Fir,.  339. — Purkinje  Cell  of  .\dull  Human  Cerebellum.  Golgi  preparation.  (Cajal.) 
a,  .\xone;  b,  recurrent  collateral;  d,  spaces  occupied  by  basket  cells;  c,  spaces  occupied  by 
blfK^d-vesscls. 


given  ofi'  from  the  end  opposite  to  the  dendrites  and  passes  through 
the  granular  layer  into  the  white  matter,  either  to  one  of  the  internal 
cerebellar  nuclei  where  it  terminates,  or  to  some  other  part  of  the 
cortex.  The  I'urkinje  cells  are  almost  the  only  cells  the  axones  of 
which  enter  the  white  matter.  It  is  evident  that  all  intracortical 
connections  must  ultimately  converge  on  these  cells  to  reach  the 
efferent  cerebellar  i)aths.  The  axones  of  the  J'urkinje  cells  give  off 
collaterals  not  far  from  their  (origin,  which  ])ass  into  the  molecular 
layer  and  ai)pear  to  terminate  there  in  end    "buttons"  upon  the 


510 


THE  ORGANS 


bodies  of  adjacent  Purkinje  cells.  The  medullated  axones  form  the 
coarser  fibres  traversing  the  granular  layer.  The  cell  body  is  fairly 
well  filled  with  small  chromophilic  bodies  of  uniform  size,  often  show- 
ing a  slightly  concentric  arrangement  (Fig.  3.38). 

The  cells  in  the  molecular  layer  (stellate  cells)  are  either  superficial 
stellate  cells  with  irregular  branching  dendrites  and  a  short  axone  or 
deep  stellate  {basket)  cells.  These  latter  are  cells  the  axones  of  which 
(apparently  non-medullated)  have  a  narrow  neck  and  unusual  thicken- 
ing beyond  the  neck.     They  extend  at  right  angles  to  the  laminae 


Fig.  340. — Section  of  Adult  Human  Cerebellum.  Silver  Method  of  Cajal.  (Cajal.) 
A,  B,  Cells  in  the  granular  layer  enveloped  by  basket  fibres;  C,  cell  of  Purkinje.  The 
axone  of  one  of  the  ceUs  of  Purkinje  is  shown. 


for  a  distance  of  several  Purkinje  cells,  giving  off  to  each  Purkinje  cell 
one  or  more  collaterals  which  pass  toward  the  granular  layer  and 
envelop,  with  their  terminal  arborizations,  the  body  and  proximal, 
non-medullated  portion  of  the  axone  of  the  Purkinje  cell.  Collaterals 
of  other  basket  cell  axones  may  terminate  around  the  same  Purkinje 
cell,  forming  the  "basket"  (Fig.  340).  The  dendrites  of  the  basket 
cells  rarnify  throughout  the  molecular  layer.  Besides  the  cells  con- 
tained in  it,  and  the  dendritic  arborizations  of  the  Purkinje  cells,  the 
molecular  layer  contains  the  axones  of  the  granule  cells  and  the  ter- 
minations of  the  chmbing  fibres  (see  below) .  In  ordinary  stains  it  pre- 
sents a  general  punctate  appearance,  with  the  scattered  nuclei  of  the 


THE  NERVOUS   SYSTEM 


511 


Fig.  341. — Diagram  of  Longitudinal  Section  of  Cerebellar  Lamin^.  Golgi  method. 
(Kolliker.)  gr,  Cell  of  the  granular  layer;  n,  axone  of  granule  cell;  n',  the  same  in  molec- 
ular layer  where  it  branches  and  runs  in  long  axis  of  lamina;  p,  Purkinje  cell  showing 
how  much  less  extensively  its  dendrites  (/>')  branch  in  long  axis  of  lamina.  (Compare 
Fig.  343-) 


':;^>fi>^-^ 


Fig.  342. — Granule  Cells  and  Mossy  Fibres  in  the  CenliLllimi  of  Adult  ('at.  Silver 
method  of  Cajal.  (Cajal.^  A,  (Jranulc  cell;  li,  (Joigi  cell;  n,  dLiidrilic  arborization  of 
granule  cell;  b,  mossy  fibres  j)assing  by  (joigi  cell;  c,  mossy  fibre;  d,  termination  oi  a 
mossy'ftbre;  e,  terminal  processes  given  ofT  from  a  thickening  in  a  mossy  fibre. 


512 


THE  ORGANS 


short  axone  and  basket  cells,  and  the  coarser  dendrites  of  the  Purkinje 
cells  distinguishable  (Fig.  338). 

The  granular  layer  with  ordinary  stains  presents  the  appearance 
of  closely  packed  nuclei  with  clear  spaces  here  and  there  {"islands^' 
or  " glomeruW)  and  also  a  few  larger  cells  (Fig.  338).  Most  of  these 
nuclei  belong  to  the  granule  cells,  which  are  caryochrome  cells.  The 
granule  cells  are  small  and  possess  three  to  six  dendrites  which  are 


Fig.  343. — Semi-diagrammatic  transverse  Section  of  a  Cerebellar  Lamina  of  a  Mam- 
mal, as  shown  by  the  Golgi  Method.  (Cajal.)  A,  Molecular  layer;  B,  granular  layer; 
C,  white  matter;  a,  Purkinje  cell,  seen  flat;  h,  basket  cells  of  the  molecular  layer;  d,  their 
terminal  arborizations  which  envelop  the  iDodies  of  the  Purkinje  cells;  e,  superficial  stel- 
late cells;/,  Golgi  cell;  g,  granule  cells  with  their  axis-cylinders  ascending  and  bifurcating 
at  i;  h,  mossy  fibres;  j,  neuroglia  cell;  m,  neuroglia  cell  in  granular  layer;  n,  climbing 
fibres. 


comparatively  short  and  terminate  in  the  glomeruli  with  a  compact 
arborization,  each  branch  of  which  ends  in  a  small  varicosity.  The 
axones  of  the  granule  cells,  which  are  non-medullated,  ascend  into  the 
molecular  layer  where  each  divides  into  two  branches  running  longi- 
tudinally along  the  laminae  and  terminating  in  varicosities  (Figs.  341, 
343).  These  are  the  parallel  fibres  of  the  molecular  layer.  They 
thus  run  at  right  angles  to  and  through  the  dendritic  expansions  of 


THE   NERVOUS   SYSTEM 


513 


the  Purkinje  cells  and  their  cross  sections  together  with  the  terminal 
dendritic  arborizations  of  the  Purkinje  cells  give  the  molecular  layer 
its  punctate  appearance.  The  scattered  larger  cells  in  the  granular 
layer  are  principally  short  axone  or  Golgi  cells,  whose  main  dendrites 
usually  penetrate  and  branch  within  the  molecular  layer.  Their 
axones  often  form  very  extensive  and  complicated  arborizations  in 
the  granular  layer,  the  terminations  of  which  are  concentrated  in 
the  glomeruli  (Fig.  343,/).  Dislocated  cells  of  this  type  may  have 
their  cell  bodies  in  the  molecular  layer. 


Fig.  344. — Cross  Section  of  a  Cerebellar  Convolution  Stained  by  Weigert's  Method, 
f  Ko.liker.)  m,  Molecular  layer;  K,  granular  layer;  w,  white  matter;  q,  fine  fibres  passing 
from  white  matter  into  the  molecular  layer;  Ir,  dots  represent  longitudinal  fibres  of  molec- 
ular layer  among  bodies  of  Purkinje  cells. 


In  the  cortex  there  are  also  the  terminations  of  the  afferent 
cerebellar  fibres  already  mentioned  (p.  507).  These  are  of  two  types, 
mossy  fibres  and  climbing  fibres.  The  mossy  fibres,  so  called  from 
the  appearance  of  their  terminations  in  embryos,  are  the  coarsest 
fibres  of  the  white  matter.  While  in  the  latter  they  bifurcate, 
branches  going  to  different  laminae.  These  main  branches  give  off 
secondary  branches  which  enter  the  granular  layer  and  there  arborize. 
Uuring  their  course,  and  also  at  their  terminations,  these  branches 
are  thickened  in  j)Iaces  and  there  give  off  short,  thick,  terminal 

3.3 


514  THE  ORGANS 

branches  which  end  in  varicosities.  These  terminal  branches  are 
located  within  the  glomeruU.  The  glomeruH  thus  contain  the 
dendritic  terminations  of  the  granule  cells,  the  axonal  terminations 
of  the  Golgi  cells,  and  the  terminations  of  the  mossy  fibres.  (Figs. 
343  and  342.) 

The  cHmbing  fibres  pass  from  the  white  matter,  through  the 
granular  layer  to  the  cells  of  Purkinje.  Passing  by  the  bodies  of  the 
latter  they  arborize  into  terminals  which  envelop  the  smooth  dendritic 
branches  of  the  Purkinje  cells;  i.e.,  all  but  the  terminal  dendritic 
arborizations.  (Fig.  343,  n).  Three  kinds  of  fibres  thus  terminate 
around  the  Purkinje  cells;  the  granule  axones,  probably  in  contact 
with  its  terminal  dendritic  arborizations;  the  climbing  fibres  around 
its  coarser  dendritic  branches;  and  the  basket  fibres  around  its 
body.  The  respective  sources  of  the  mossy  and  chmbing  fibres  are 
unknown.  There  is  some  evidence  that  the  chmbing  fibres  are 
from  the  pons. 

It  is  evident  from  the  above  that  all  of  the  cells  of  the  cerebellar 
cortex  except  the  Purkinje  cells  are  association  cells  of  the  cortex. 

The  medullated  fibres  of  the  cerebellum  (Fig.  344)  pass  from 
the  white  matter  into  the  granular  layer  and  ramify  throughout 
the  latter,  forming  quite  a  dense  plexus  separating  groups  of  granule 
cells.  Sometimes  straight  fibres  can  be  seen  passing  through  toward 
the  molecular  layer  which  are  probably  either  the  climbing  fibres  or 
axones  of  the  Purkinje  cells.  Beneath  and  between  the  bodies  of  the 
Purkinje  cells  is  a  plexus  of  fibres  extending  into  the  deeper  part  of 
the  molecular  layer,  the  remainder  of  this  layer  containing  few  or  no 
medullated  fibres.  These  fibres  in  the  vicinity  of  the  Purkinje  cells 
are  probably  principally  formed  by  the  recurrent  collaterals  of  the 
Purkinje  cells  already  mentioned.  The  remaining  fibres  of  the 
granular  plexus  would  apparently  consist  of  the  arborizations  of 
mossy  fibres  and  of  the  Golgi  cells.  Whether  the  former  are  medul- 
lated is,  however,  somewhat  uncertain. 

Most  of  the  neuroglia  cells  in  the  cerebellum  are  of  the  same 
general  type  as  seen  elsewhere,  but  in  the  Purkinje  cell  layer  are 
apparently  epithehal-like  cells  which  send  vertical  processes  to  the 
periphery.  Some  of  these  processes,  as  seen  in  the  Golgi  method, 
are  rough  and  branched,  others  are  smooth.  In  ordinary  stains 
these  processes  are  sometimes  visible  and  are  known  as  the  fibres 
of  Bergmann.     (Figs.  338,  343.) 


THE   NERVOUS   SYSTEM  515 

Isthmus 
PRACTICAL  STUDY 

9.  Transverse  Section  through  the  Isthmus  at  the  Exit  of  Nerve  IV  (Trochlearis) 

(Figs.  324  and  345) 

In  this  there  are  to  be  distinguished  three  parts,  the  thin  roof  (superior  medul- 
lary velum),  the  tegmentum  and,  ventral  to  the  latter,  the  pons.  The  tegmentum 
consists  essentially  of  the  reticular  formation,  efferent  cerebellar  and  midbrain 
connections,  and  externally  the  afferent  pallial  connections.  The  pons  contains 
the  eff'erent  pallial  paths  to  the  cerebellum  and  to  parts  of  the  nervous  system 
caudal  to  it.  The  cavity  is  the  iter  or  agnceductus  Sylvii.  Next  to  this  is  the 
central  gray  of  the  brain  wall. 

Efferent  Peripheral  Neurones. — The  root  fibres  of  the  IV  are  seen  in  the  roof. 
They  originate  from  nuclei  lying  further  forward  in  the  ventral  part  of  the  central 
gray.  The  fibres  pass  from  the  nuclei  dorsally  and  caudally  in  the  outer  part  of 
the  central  gray  and  finally  decussate  in  the  roof  and  emerge.  It  is  only  the 
latter  part  of  this  course  which  is  seen  in  this  level. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — The  mesen- 
cephalic root  of  the  V  lies  in  the  lateral  part  of  the  central  gray.  Mingled  with 
its  fibres  may  be  seen  the  rounded  cells,  the  axones  of  which  form  these  fibres. 

The  lateral  lemniscus  occupies  part  of  the  lateral  swelling  on  the  surface  of  the 
tegmentum,  forming  the  major  part  of  the  external  structure  known  as  the  trigo- 
num  lemnisci.  Groups  of  cells  among  its  fibres  constitute  the  dorsal  nucleus  of 
the  lateral  lemniscus.  The  medial  lemniscus  is  now  still  more  flattened.  The 
spino-thalamic  tract  is  in  about  the  same  position,  between  the  two  lemnisci. 
Thus  at  this  level,  the  principal  afferent  suprasegmental  paths  form  an  L-shaped 
mass,  enveloping  the  rest  of  the  tegmentum  and  representing  general  bodily 
sensation  and  hearing.  There  are  also  cranial  nerve  ascending  paths  lying 
probably  within  the  reticular  formation  and  fillet  (secondary  vago-glossopharyn- 
geal  and  trigeminal  tracts,  representing  visceral,  taste,  and  general  head  sen- 
sation).   These  cannot  be  distinguished  in  the  section. 

The  ventral  spino-cerebellar  tract  is  on  the  surface,  and  now  comes  to  lie 
external  to  the  superior  cerebellar  peduncle.  At  about  this  point  it  turns 
caudally,  and  passes  back  into  the  cerebellum,  accompanying  the  superior 
peduncle. 

Otl  er  Afferent  Cerebellar  Connections. — 'J'hc  central  tegmental  tract  oc- 
cupies the  same  position.  (For  the  pallio-cercbelhir  connection  sec  "Efferent 
Suprasegmental  Neurones"  below.) 

Intersegmental  Neurones.— 'J'hc  reticular  formation  is  diminished  in  extent. 
One  of  its  nuclei,  the  nucleus  centralis  superior,  lies  near  the  raphe.  The  rubro- 
spinal tract  has  moved  somewhat  mesially.  It  is  dorsal  to  the  medial  lemniscus. 
The  merlial  longitudinal  fasciculus  is  in  the  same  position,  and  is  a  well-marked 
bundle  lying  at  the  bounflary  bet  ween  the  ventral  part  of  the  central  gray  and  the 
reticular  formal  ir)n. 

Efferent  Suprasegmental  Neurones.  —The  f)yramids  arc  now  broken  up  into 
bunrlles  which  may  .show  a  tendency  to  gather  in  the  ventral  part  of  the  pons 


516 


THE  ORGANS 


THE  NERVOUS  SYSTEM  517 

(distinguishable  in  one-month  infant,  where  thej^  are  meduUated  while  the  pallio- 
pontile  system  is  not).  Bundles  apparently  forming  lateral  and  mesial  portions 
of  the  medial  lemniscus  (not  indicated  in  the  figure)  are  aberrant  efferent  pallial 
fibres.  Such  bundles  have  been  seen  passing  from  pons  to  tegmentum  and 
also  imbedded  in  the  medial  lemniscus  in  lower  levels  (pp.  501,  491).  Some  of 
these  fibres  are  possibly  fibres  acting  directly  or  indirectly  on  the  efferent  periph- 
eral neurones  or  motor  nuclei  of  the  cranial  nerves  (see  p.  521). 

The  pallio-pontile  fibres  are  still  more  numerous.  The  gray  matter  in  the 
pons  (nuclei  pontis)  is  very  extensive.  The  transverse  fibres  of  the  pons  no 
longer  pass  at  this  level  into  the  cerebellum,  but  are  collected  at  the  sides  of  the 
p>ons  to  pass  backward  to  the  cerebellum  (compare  with  an  external  view  of  the 
brain). 

The  superior  cerebellar  peduncles  or  brachia  conjunctiva  are  two  large 
crescentric  bundles  of  fibres  in  the  lateral  part  of  the  reticular  formation. 
Some  of  their  fibres  have  begun  to  decussate  in  the  ventral  part  of  the  reticular 
formation. 

The  colliculo-spinal  tract  or  predorsal  fasciculus  lies  ventral  to  the  medial 
longitudinal  fasciculus. 


Midbrain  or  Mesencephalon 

The  dorsal  surface  of  the  midbrain  presents  four  rounded  promi- 
nences, the  two  inferior  and  two  superior  colHculi  (posterior  and 
anterior  corpora  quadrigemina) .  Ventrally  are  seen  two  diverging 
masses  of  longitudinal  fibres,  the  pes  peduncuh,  separated  by  a  deep 
groove  or  sulcus.  In  the  midbrain  are  to  be  distinguished,  (a)  the 
expanded  roof,  the  colliculi  or  corpora  quadrigemina^  {h)  the  tegmentum 
containing  the  segmental  (cranial  nerves  IV  and  III)  and  interseg- 
mental apparatus  and  the  afferent  suprasegmental  paths,  and  (c)  the 
basis  pedunculi,  ventral  to  the  tegmentum  and  comprising  the 
principal  efferent  paUial  paths  {pes  pedunculi)  and  the  substantia 
nigra. 

The  cavity  of  the  midbrain  is  the  aqueduclus  Sylvii  or  iter. 

PRACTICAL  STUDY 

10.  Transverse  Section  through  Midbrain  at  Level  of  Superior  Colliculi  (An- 
terior Corpora  Quadrigemina)  and  Exit  of  Nerve  III  (Oculomotor)      (Figs. 

.^24  and  347) 

Compared  with  the  f)rcceding  section,  the  following  arc  the  most  conspicuous 
changes:  The  roof  has  now  enlarged  into  the  superior  colliculi;  the  tegmentum 
now  contains  the  nuclei  and  roots  of  nerve  III  and  the  red  nucleus;  instead 
of  the  pons,  the  ventral  part  (jf  the  brain  is  now  composed  of  the  basis  i)edunculi, 
consi.sting  of  a  mass  of  elTerent   |)allial  iilires  and  I  he  subsfanlia  nigra.       I'he 


518 


THE  ORGANS 


term  crura  cerebri  or  cerebral  peduncles  is  loosely  used  to  include  all  except 
the  roof  of  the  brain  at  this  level,  i.e.,  tegmentum  and  basis  pedunculi. 

Efferent  Peripl  eral  Neurones. — The  nucleus  of  nerve  III  or  oculomotor  nucleus 
is  located  in  the  ventral  part  of  the  central  gray  in  a  V-shaped  trough  formed  by 
the  fibres  of  the  medial  longitudinal  fasciculus.  The  nucleus  is  divided  into  large 
and  small-celled  groups.    The  large-celled  groups  are  two  lateral  groups  subdivided 


i^ni£S£"^y^g^^^v^^ 


Fig.  346. — The  region  of  the  aquseductus  Sylvii  seen  from  above.  Schema 
showing  the  position  of  the  nuclei  of  nerves  III  and  TV  and  their  subdivisions.  (Edinger.) 
I.  The  small-celled  nucleus  (here  represented  as  one  on  each  side)  a,  its  ciliary,  b,  its 
pupillary  portion.  2,  The  portion  of  the  large-celled  nucleus  sending  uncrossed  fibres 
to  M.  levator  palpebrae;  3,  portion  sending  uncrossed  fibres  to  M.  rectus  superior;  4 
and  5,  portions  sending  crossed  and  uncrossed  fibres  to  Mm.  rectus  internus  and 
obliquus  inferior;  6,  portion  sending  crossed  fibres  to  M.  rectus  inferior.  The  nucleus 
trochlearis  sends  crossed  fibres  to  M.  obliquus  superior. 

into  anterior  and  posterior  dorso-lateral  and  anterior  and  posterior  ventro-mesial, 
and  a  central  or  median  group — nine  in  all.  Between  the  cephalic  or  anterior 
groups  are  on  each  side  a  small-celled  group  known  as  the  Edinger-Westphal 
nucleus,  and  still  further  forward  are  two  small-celled  anterior  median  nuclei. 
The  connections  of  these  groups  with  the  extrinsic  muscles  of  the  eye  innervated 
by  nerve  III  (internal,  superior  and  inferior  recti,  and  inferior  oblique)  and  the 
levator  palpebrae    superioris   and  intrinsic  eye  muscles  (ciliary  and  sphincter 


THE  NERVOUS  SYSTEM 


519 


520  THE  ORGANS 

pupillae,  via  ciliary  sympathetic  ganglion)  are  uncertain.  From  a  priori  grounds, 
the  innervation  of  the  intrinsic  muscles  by  the  small-celled  groups  and  the  other 
muscles  by  the  large-celled  groups  would  seem  probable.  Some  of  the  fibres, 
usually  stated  to  be  from  the  posterior  dorsal-lateral  group,  decussate.  Recent 
observations  (Cajal)  would  indicate  that  the  decussating  fibres  come  from  the 
ventro-mesial  lateral  groups.  What  is  perhaps  the  prevailing  view  as  to  these 
relations  is  shown  in  Fig.  346.  The  various  fibres  pass  ventrally  in  a  number  of 
bundles,  some  passing  mesial  to,  some  traversing,  and  some  passing  lateral  to 
the  superior  cerebellar  peduncle  and  red  nucleus.  Ventral  to  these  the  root 
fibres  come  together  and  emerge  on  the  ventral  aspect  of  the  midbrain  (Figs. 
347  and  348.) 

The  nucleus  of  nerve  III  receives  terminals  and  collaterals  from  the  medial 
longitudinal  fasciculus,  i.e.,  from  the  ascending  axones  from  Deiters'  nucleus  and 
the  descending  axones  from  the  nucleus  of  the  medial  longitudinal  fasciculus, 
possibly  collaterals  from  the  coUiculo-spinal  tract,  collaterals  or  terminals  from 
the  superior  cerebellar  peduncle  and  from  the  reticular  formation.  Its  exact 
relation  to  efferent  pallial  fibres  is  not  known.  Fibres  in  the  medial  longitudinal 
fasciculus  connect  the  nuclei  of  III,  IV  and  VI  (synergic  movements  of  eye 
muscles) . 

Immediately  caudal  to  the  nucleus  of  nerve  III  (not  in  the  plane  of  the 
section)  is  the  nucleus  of  the  nerve  IV  occupying  a  position  similar  to  the  lateral 
groups  of  the  nerve  III  nucleus.  The  course  of  the  root  fibres  of  the  IV  has  been 
mentioned  (preceding  section).  It  receives  terminals  similar  to  those  received 
by  III. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — The  mesen- 
cephalic trigeminal  root  is  sometimes  distinguishable  on  the  lateral  border  of  the 
central  gray. 

The  lateral  lemniscus  has  partly  or  wholly  terminated  in  the  inferior  coUiculus 
at  a  lower  level.  Fibres  from  the  latter  form  its  arm  or  brachium,  representing 
another  link  of  the  cochlear  path.  In  the  present  section  the  fibres  of  the 
brachium  of  the  inferior  coUiculus  are  seen  entering  the  medial  geniculate  body 
(which  is  a  part  of  the  thalamus) .  Axones  of  the  cells  of  this  body  constitute  the 
last  relay  of  the  cochlear  path  (III,  p.  476)  to  the  temporal  cortex  cerebri  (not 
present  in  this  section).  As  already  stated,  there  is  doubt  as  to  how  far  this 
path  is  interrupted  in  various  nuclei  along  its  course  such  as  the  superior  olives, 
trapezoid,  lateral  lemniscus  nucleus  and  inferior  coUiculus.  It  may  be  reducible 
to  three  principal  neurone  groups:  (i)  the  spinal  ganglion  and  its  cochlear  nerve, 
(2)  the  lateral  lemniscus  and  (3)  the  geniculo-temporal  system. 

The  medial  lemniscus  is  now  a  laterally  placed,  curved  bundle,  displaced 
laterally  by  the  red  nucleus.  According  to  some  authorities,  some  of  its  fibres 
terminate  in  the  superior  coUiculus.  The  spino-thalamic  tract  is  plainly  distin- 
guishable as  a  bundle  dorsal  to  the  dorsal  edge  of  the  medial  lemniscus.  At  this 
level,  then,  the  afferent  paths  from  cord  to  pallium  have  practically  united. 

In  the  superior  coUiculus  are  terminations  of  the  optic  tract  (the  continuation 
past  the  optic  chiasma  of  the  so-called  optic  nerve)  (see  below). 

The  central  tegmental  tract  is  displaced  dorsally  by  the  red  nucleus. 

Intersegmental  Neurones. — The  reticular  formation  is  smaller.     The  rubro- 


THE  NERVOUS  SYSTEM  521 

spinal  tract  (not  distinguishable)  is  emerging  from  its  nucleus  of  origin,  the 
nucleus  ruber.  Just  below  this  level  its  fibres  decussate  {ventral  decussation  of 
Forel)  and  pass  to  the  location  they  have  been  seen  to  occupy  in  preceding  levels. 
The  nucleus  ruber  or  red  nucleus  is  very  conspicuous,  occupying  a  large  part  of 
the  reticular  formation.  It  consists  of  a  large-celled  part  which  gives  rise  to  the 
rubro-spinal  tract  and  to  rubro-bulbar  fibres,  and  a  smaller-celled  portion. 
The  latter  sends  fibres  to  the  thalamus  and  thence  to  the  pallium.  The  nucleus 
ruber,  probably  the  first  named  part,  also  receives  fibres  from  the  pallium. 
According  to  this  it  will  be  seen  that  the  nucleus  ruber  is  a  part  of  the  descend- 
ing cerebello-rubro-bulbar  and  spinal  path  (XVII,  p.  478),  of  the  cerebello- 
pallial  path  (MI,  p.  477),  and  of  the  pallio-rubro-bulbar  and  spinal  path  (XIV, 
p.  477).  The  red  nucleus  probably  also  receives  collaterals  from  the  coUiculo- 
spinal  tract. 

The  medial  longitudinal  fasciculus  is  diminished,  some  of  its  descending 
fibres  having  been  formed  from  reticular  formation  nuclei  below  this  level. 
Many  of  its  fibres,  both  ascending  and  descending,  send  collaterals  and  terminals 
to  the  cells  of  the  oculomotor  nucleus. 

Efferent  Suprasegmental  Neurones. — The  ventral  part  of  the  brain  is  com- 
posed of  a  mass  of  efferent  pallial  fibres,  the  pes  pedunculi.  The  pyramidal  fibres 
from  the  precentral  areas  of  the  cerebral  hemisphere  (pallio-spinal  and  some 
pallio-bulbar  fibres)  occupy  about  the  middle  three-fifths,  but  are  also  scattered 
through  other  parts  of  the  pes,  especially  the  mesial  part.  The  leg  fibres  are 
probably  more  numerous  laterally,  the  arm  fibres  in  the  middle,  and  the  face  fibres 
mesially.  In  the  lateral  part  of  the  pes  are  pallio-pontile  fibres  from  the  occipital 
and  temporal  lobes  of  the  cerebral  hemispheres  (occipito-temporal  pallio-pontile 
fibres).  In  the  mesial  part  are  efferent  pallial  fibres  from  the  frontal  lobe,  in  part 
to  the  pons  nuclei  (frontal  pallio-pontile)  and  in  part  possibly  from  the  lower 
frontal  region  to  the  motor  nuclei  of  cranial  nerves  VII  and  XII.  Besides  the 
above  pallio-pontile  and  pallio-spinal  fibres  in  the  pes  there  are  two  other 
aberrant  peduncular  bundles  (p.  517)  which  probably  contain  efferent  pallial 
fibres  which  pass  to  the  motor  nuclei  of  nerves  V,  VII  and  XII.  These  two 
bundles,  which  may  be  termed  the  mesial  and  lateral  pcdunculo-tegmental 
bundles  ("medial  accessory  fillet"  and  "lateral  peduncular  fillet")  detach  them- 
selves from  the  pes  higher  up,  and  below  this  level  come  to  lie  in  the  vicinity 
of  the  medial  lemniscus. 

Dorsal  to  the  pes  and  constituting  the  remainder  of  the  l^asis  pedunculi  is  a 
mass  of  gray  matter  which,  on  account  of  the  pigmentation  of  its  cells,  is  known 
as  the  substantia  nigra.  The  substantia  nigra  receives  collaterals  from  the  ad- 
joining pes  fibres.  These  arc  probably  fibres  from  the  motor  cortex  but  according 
to  some  may  be  from  the  corpus  striatum  or  corpus  suhthalamicum.  The 
axoncs  of  the  cells  of  the  substantia  nigra  enter  the  tegmentum.  Their  des- 
tination is  unknown. 

The  superior  cerebellar  peduncle  has  completed  its  decussation  below  this 
level  and  its  fibers  are  seen  surrounding  or  within  the  nucleus  ruber  which  is  one 
of  their  terminal  nuclei.  Other  fibres  of  the  superior  cerebellar  peduncle 
terminate  in  the  thalamus  and  some  are  stated  to  terminate  in  the  nucleus 
of  nerve  III. 


522  THE  ORGANS 

Internal  arcuate  fibres  from  the  gray  matter  of  the  superior  colliculus  pass 
through  the  reticular  formation,  and  form  an  oblique  decussation.  This 
decussation  is  the  dorsal,  or  fountain-like  decussation  of  Meynert.  The  fibres 
originate  from  cells  in  the  superior  colliculus  (tectum  opticum),  and  after 
decussation  form  the  descending  colliculo-hulbar  and  spinal  tract  (tecto-spinal 
or  predorsal  tract)  (see  also  below). 

The  Anterior  Corpus  Quadrigeminum  or  Superior  CoUicixlus. — In  this  four 
principal  layers  may  be  distinguished  besides  the  usual  covering  of  neuroglia 
cells  and  fibres:  (i)  An  outer  white  layer,  stratum  zonale.  This  consists  of  fine 
nerve  fibres  coming  from  the  superior  brachium,  possibly  fibres  from  the  optic 
tract  and  cerebral  cortex.  Among  them  are  small  nerve  cells,  mostly  horizontal 
and  with  tangential  or  centrally  directed  axones.  (2)  A  gray  layer,  the  stratum 
cinereum.  This  consists  of  radially  arranged  nerve  cells  with  their  larger  den- 
drites proceeding  outward,  and  their  axones  inward.  The  largest  cells  lie  deep- 
est. In  this  layer  the  optic  fibers  principally  terminate.  (3)  The  stratum 
opticum  consists  principally  of  optic  fibres  which  send  their  terminals  mostly 
into  the  preceding  layer,  but  also  into  the  deeper  layers.  It  also  contains  cells 
whose  axones  pass  into  the  next  layer.  (4)  Deep  gray-white  layer,  or  stratum 
lemnisci,  because  it  is  stated  to  contain  fibres  from  the  medial  lemniscus  which 
terminate  in  the  superior  colliculus  (denied  by  some).  This  layer  contains  large 
and  medium  stellate  cells  whose  axones,  together  with  axones  from  cells  in 
the  more  superficial  layers,  either  pass  across  to  the  opposite  colliculus  or 
sweep  ventrally  around  the  central  gray,  decussate  in  the  raphe  and  proceed 
caudally  as  the  colliculo-bulbar  and  spinal  tract.  The  above  relations  have 
been  principally  ascertained  by  the  Golgi  method.  The  superior  colliculus 
also  possibly  receives  fibres  from  the  lateral  lemniscus  and  spino-thalamic  tract . 
It  also  receives  fibres  from  the  occipital  and  temporal  cortex  cerebri  (pallio- 
collicular  fibres). 

Belonging  to  the  midbrain  is  the  posterior  commissure  (not  in  the  section)  the 
fibres  of  which  cross  in  the  roof  just  anterior  to  the  superior  colliculus.  Its 
fibres  originate  from  coUicular  cells  (in  turn  receiving  optic  fibres),  decussate  and 
terminate  in  the  nucleus  of  the  medial  longitudinal  fasciculus  and  other  nuclei 
in  the  reticular  formation. 

The  colliculus  thus  consists  essentially  of  (o)  afferent  fibres  from  the  retina 
(optic  tract),  the  pallium  and  possibly  other  parts  of  the  nervous  system,  and  (&) 
efferent  neurones  to  other  parts  of  the  brain  and  cord  brought  into  various 
relations  with  each  other  in  the  colliculus  either  directly  or  by  (c)  the  association 
cells  of  the  colliculus,  the  axones  of  which  do  not  leave  the  latter. 

Forebrain  or  Prosencephalon 

Inteebrain  (diencephalon  or  thalamencephalon) 

In  the  interbrain  or  diencephalon,  three  parts  may  be  distin- 
guished; the  thalamus,  epithalamus,  and  hypothalamus.  The  epithala- 
mus  consists  principally  of  the  pineal  body,  the  habenulae,  and  striae 
thalami.     The  hypothalamus  consists  mainly  of  the  structures  in 


THE  NERVOUS  SYSTEM  523 

the  ventral  expansion  of  the  interbrain,  such  as  the  corpora  mamil- 
laria,  tuber  cinereum,  infundibulum  and  posterior  lobe  of  the  hy- 
pophysis. The  epithalamus  and  hypothalamus  are  principally  con- 
nected with  olfactory  paths  (see  p.  530  and  Fig.  351).  Certain 
extensions  forward  of  the  tegmentum  are  also  termed  subthalamic 
(e.g.,  corpus  subthalamicum  or  corpus  Luysii). 

The  thalamus  comprises  the  great  bulk  of  the  interbrain.  It  con- 
sists of  a  number  of  nuclei  forming  links  in  afTerent  and  efferent 
pallial  paths  and  of  other  nuclei  connected  with  the  corpora  striata. 
There  is  much  difference  of  opinion  both  as  to  the  number  of  the  nuclei 
and  their  connections.  According  to  some  authorities  the  thalamus 
may  be  regarded  as  divided  into  internal  and  external  segments 
(usually  separated  by  the  lamina  medullaris  medialis).  The  in- 
ternal segment  consists  of  an  anterior  nucleus,  median  nucleus,  the 
"median  center"  or  nucleus  of  Luys,  and  a  nucleus  arcuatus.  The 
external  segment  consists  of  a  dorso-lateral,  an  external  ventro- 
lateral, an  internal  ventro-lateral,  and  a  ventral  nucleus.  To  the 
external  segment  should  be  added  the  pulvinar  and  lateral  and 
medial  geniculate  bodies  (metathalamus).  The  various  nuclei  of 
this  external  segment  receive  the  fibres  of  the  afferent  pallial  paths 
and  complete  the  paths  by  sending  fibres  to  the  cortex  palhi.  These 
paths  are  (i)  the  medial  lemniscus,  spino-thalamic,  and  secondary 
trigeminal  tracts  (general  sensory  from  body  and  face)  to  the  ventro- 
lateral nuclei  and  thence  to  the  cortex  of  the  central  region  of  the 
paUium;  (2)  the  lateral  fillet  or  brachium  of  inferior  colliculus  (hearing) 
to  the  medial  geniculate  body,  and  thence  to  the  temporal  region  of 
the  pallium;  (3)  the  optic  tract  to  the  lateral  geniculate  body  and 
thence  to  the  occipital  pallial  cortex;  (4)  part  of  the  superior  cere- 
bellar peduncle  (also  said  to  be  distributed  to  nuclei  of  inner  segment). 
The  visceral  (including  gustatory)  and  vestibular  paths  to  the  pallium 
are  not  definitely  known.  (See  also  p.  475.)  As  the  olfactory  nerve 
belongs  to  the  endbrain,  its  path  to  the  pallium  does  not  traverse  the 
thalamus.  Besides  giving  rise  to  the  above  thalamo-cortical  fibres, 
the  external  thalamic  segment  in  all  probability  receives  many  de- 
scending fibres  from  the  cortex  i)allii.  The  various  fibres  connecting 
thalamus  and  cortex  constitute  the  thalamic  radiations.  In  general 
the  anterifjr  parts  of  the  cortex  are  connected  with  the  anterior  part 
of  the  external  thalamic  segment,  the  middle  with  the  middle,  and 
the  posterior  with  the  posterior.  It  is  also  probable  that  the  thalamo- 
cortical fibres  from  the  various  lateral  nudei  arc  arranged  dorso- 


524  THE  ORGANS 

ventrally,  so  that  the  fibres  from  the  ventral  parts  pass  to  the 
ventral  part  of  the  central  region  of  the  pallium,  dorsal  to  dorsal, 
etc.     (E.  Sachs.) 

The  nuclei  of  the  internal  segment  of  the  thalamus  do  not  appear, 
according  to  some  recent  researches,  to  have  direct  connections  with 
the  cortex  pallii.  The  anterior  nucleus  receives  the  bundle  of  Vicq  d' 
Azyr  (mamillo-thalamic  tract)  and  probably  sends  fibres  to  the 
nucleus  caudatus  (see  p.  533).  It  thus  belongs  to  the  olfactory 
apparatus.  The  median  nucleus  is  also  probably  connected  with 
the  nucleus  caudatus.  The  median  center  of  Luys  and  the  nucleus 
arcuatus  send  fibres  to  adjoining  thalamic  nuclei,  especially  the  lateral 
nuclei,  and  appear  to  be  thus  association  nuclei.  Other  authorities 
affirm  that  ascending  tracts  are  received  by  some  of  these  internal 
nuclei  and  that  they  have  direct  cortical  connections.  Descending 
tracts  coming  directly  from  the  thalamus  have  not  been  definitely 
demonstrated. 

PRACTICAL  STUDY 

1 1 .  Transverse  Section  through  the  Jvinction  of  Midbrain  and  Thalamus. 

(Figs.  324  and  348.) 

The  most  conspicuous  change  from  the  last  section  is  the  appearance,  or 
increase,  of  the  geniculate  bodies  and  pulvinar,  and  the  thalamic  radiations. 

Efferent  Peripheral  Neurones. — The  nuclei  and  root  fibres  of  the  III  nerve 
are  stUl  present. 

Afferent  Roots,  their  Terminal  Nuclei,  Secondary  Tracts,  and  Tertiary 
Neurones. — The  fibres  of  the  optic  tract  (optic  "nerve")  are  seen  entering  the 
ventral  surface  of  one  of  their  terminal  nuclei,  the  lateral  or  external  geniculate 
body.  Other  optic  fibres  (not  entirely  traceable)  enter  the  pulvinar  thalami  and 
the  superior  coUiculus  {Strd)  (see  also  preceding  section).  On  the  dorso-lateral 
surface  of  the  lateral  geniculate  body,  a  bundle  of  fibres  accumulates  which 
represents  the  beginning  of  the  geniculo-calcarine  tract  to  the  occipital  cortex, 
thereby  completing  the  visual  path. 

Internal  to  the  lateral  geniculate  body  is  the  medial  (internal)  geniculate  body 
which  now  contains  the  terminals  of  the  brachium  of  the  inferior  coUiculus. 
Fibres  from  its  cells  gather  on  its  lateral  surface.  These  represent  the  beginning 
of  the  geniculo-temporal  tract  to  the  temporal  cortex,  thereby  completing  the 
auditory  path. 

Internal  and  ventral  to  the  medial  geniculate  body  are  the  medial  lemniscus 
(bulbo-thalamic)  and  spino-thalamic  tracts  about  to  terminate  in  the  ventro- 
lateral thalamic  nuclei  whose  axones  complete  the  general  sensory  path  by  passing 
to  the  central  cortex. 

The  central  tegmental  tract  can  hardly  be  distinguished. 
'  Intersegmental  Neurones. — The  nucleus  ruber  is  still  large,  but  the  remainder 


THE  NERVOUS  SYSTEM 


525 


V 


be—  -—  "T  C>  c  •-    tn 

f  2;i5^^'3:^  E  ?  3 

3    5    D    O    S:      .  -^  >-    O;^ 

ft;  c  aTi  "  5  Ji  «'S  "1 
•si  o  ^^  g  ^  ^  - '-S  o. 

^  ^  c  g 


i'o 


3',_0    U<i^*Jr7 

"i^^"rt  S^  3^.S 


fo^ 


•C  I-  .h  ^  —  o  ^ 

y  J  .5  ;=  5^:::  3  .^ -3  8 


,^  „  G  t"  ij '    ^   . 

<-i         c    _    ^ 


«- 


g    OJ 


C  ,1J    rt  .S    "5    3 
2'^ -3    p    ^3 

V  >~H  '2    3    V)  "G  ^^    i'n         -t;  TJ 
'.  '~-itC~rtrtr~"^'^     -Oi 

■^    « s  ^  "^.^  "S  r:  >  i?) 


!tq 


-^j' 


pc  !_.   k<  "  ^*  ,•  ^  i3       q 
C3pj3-!2--^tf,3  e  J 

^  S  S--y.H  S-S  °  3  2:3 


a.0  S 


526  THE  ORGANS 

of  the  reticular  formation  has  nearly  disappeared.  The  medial  longitudinal 
fasciculus  is  much  diminished  as  its  ascending  fibres  terminate  in  the  nucleus  of 
nerve  III  and  many  of  its  descending  fibres  originate  from  cells  below  this  level. 
Efferent  Suprasegmental  Neurones. — The  pes  pedunculi  occupies  the  same 
position,  and  dorsal  to  it  is  the  diminished  substantia  nigra.  Along  the  ventro- 
mesial  border  of  the  pes  a  bundle  of  fibres  can  sometimes  be  distinguished 
(Fig.  348,  Lmp),  which  at  lower  levels  comes  to  lie  mesial  to  the  medial 
lemniscus  (aberrant  peduncular  fibres,  comp.  p.  521).  Descending  pallial 
fibres  (not  distinguishable)  also  probably  form  part  of  the  thalamic  radiations 

(PP-  523,  53°)- 

Fibres  of  the  superior  cerebellar  peduncle  may  be  seen  within  and  around 
the  nucleus  ruber.  Some  of  these  terminate  in  the  latter,  some  pass  further 
forward  to  end  in  the  thalamus  (compare  pp.  507,  521). 

The  Superior  Colliculus  is  somewhat  diminished.  The  posterior  commissure 
passes  across  in  the  roof  dorsal  to  the  central  gray  (see  preceding  section) . 

The  Thalamus  (can  hardly  be  included  under  the  preceding  structures). — 
The  corpora  geniculata  have  been  mentioned.  The  puhinar  thalami  is  a  large 
gray  mass  dorsal  to  the  medial  geniculate  body.  Fibres  passing  laterally  from  it 
contribute  to  the  retrolenticular  portion  of  the  internal  capsule  {Cirl) .  These  fibres 
are  a  part  of  the  thalamic  radiations. 

The  nucleus  caudatus  (a  portion  of  the  corpus  striatum  of  the  endbrain)  is 
present. 

12.  Section  through  the  Interbrain  at  the  Level  of  the  Optic  Chiasma. 
(Figs.  324  and  349.) 

Efferent  Peripheral  Neurones. — None  present. 

Afferent  Roots,  their  Terminal  Nuclei,  Secondary  Tracts,  and  Tertiary 
Neurones. — Fibres  of  the  optic  nerve  are  seen  decussating  and  forming  the  optic 
chiasma.  The  further  continuation  of  the  optic  fibres  to  their  termination  is 
called  the  optic  tract.  Both  nerve  and  tract  constitute  the  secondary  optic  tract, 
the  optic  chiasma  being  analogous  to  the  decussation  of  the  medial  lemniscus  and 
of  the  lateral  lemniscus  (trapezius).  (For  further  description  of  optic  paths  see 
Fig-  350.) 

The  medial  lemniscus,  spino-thalamic,  and  secondary  trigeminal  tracts  are 


Fig.  349. — Section  through  the  Interbrain  at  the  Level  of  the  Optic  Chiasma.  (The 
chorioid  plexus  of  the  third  ventricle  has  been  removed.)  Weigert  preparation.  (Mar- 
burg) Ce,  capsula  externa;  Cex,  capsula  extrema;  Chll,  chiasma  nervorum  opticorum 
(or  optic  chiasma);  Ci,  capsula  interna;  CI,  claustrum;  Cml,  ganglion  laterale  corp. 
mammillaris;  Cmm,  ganglion  mediale  corp.  mammilL;  Coa,  commissura  anterior;  Cospm, 
commissura  supramammillaris;  Cstk,  corpus  subthalamicum;  e,  nucleus  externus  gangl. 
med.  corpor.  mammillaris;  Fmp,  fasciculus  mammillaris  princeps;  Fo,  fornix;  Fp,  fibr^e 
perforantes  (pedunculi) ; /r/!/,  fasciculus  retroflexus  (Meynert);  Fsp,  fasciculus  subthal- 
amico-peduncularis;  Fu,  fasciculus  uncinatus;  Ghb,  ganglion  habenulae;  glp,  globus  palli- 
dus;  H,  area  tegmenti  Forel;  HI,  pars  dorsalis  arese  tegmenti;  HII,  pars  ventralis  areae 
tegmenti;  I,  insula  Reillii;  i,  nucleus  internus  gangl.  medial,  corp.  mammillaris;  Lml, 
lamina  meduUaris  lateralis;  Narc,  nucleus  arcuatus  thalami;  Nc,  nucleus  caudatus; 
NL,  nucleus  Luysii  (nucleus  centralis,  or  median  centre,  thalami;)  Nl,  nucleus  lateralis 
thalami;  Nlv,  nucleus  lateralis  ventralis  thalami;  Ntg,  nucleus  ruber  tegmenti;  Fp, 
pes  pedunculi;  Pm,  putamen;  SnS,  substantia  nigra;  St,  stria  cornea;  Strz,  stratum  zonale 
thalami;  Til,  tractus  opticus;  Tbc,  tuber  cinereum;.  Tt,  taenia  thalami;  VIII,  ven- 
triculus  tertius;  Zi,  zona  incerta. 


THE  NERVOUS  SYSTEM 


527 


Ife 


528 


THE  ORGANS 


Cotter  • 


--.fase.  lonq.hoif'. 

,    ,..'.". Nu.SlN."  I 

>^-''^~~-=--<;^ Tk  tecto-iuliaris  et  sbilJU.liS' 


Fig.  3SO. 


THE  NERVOUS  SYSTEM  529 


EXPLANATION  OF  FIG.  350. 

Fig.  350. — Diagram  of  the  Optic  (II)  Nerve  and  some  of  its  Principal  Connections. 
A,  Level  of  nerves  II  and  III;  B,  level  of  nerve  IV;  C,  level  of  nerves  VI  and  VII;  D, 
spinal  cord.     Neurone  groups  are  represented  by  one  or  several  individual  neurones. 

The  rods  and  cones  (receptors)  and  the  bipolar  cells  (  =  Neurone  No.  i)  of  the 
retina  are  not  indicated. 

Neurone  No.  2. — 2a,  Axones  of  ganglion  cells  in  temporal  part  of  retina  pass  to  pulvi- 
nar  of  thalamus  of  same  side;  2  b,  axones  of  ganglion  cells  in  temporal  retina  pass  to 
superior  coUiculus  of  same  side;  2  c,  axones  of  ganglion  cells  in  temporal  retina  pass 
to  external  geniculate  body  of  same  side;  2  e,  axones  of  ganglion  cells  in  nasal  side  of 
retina  cross  in  optic  chiasma  and  pass  to  external  geniculate  body  of  opposite  side;  2  /, 
axones  of  ganglion  cells  in  nasal  side  of  retina  cross  in  optic  chiasma  and  pass  to 
superior  coUiculus  of  opposite  side;  2  g,  axones  of  ganglion  cells  in  nasal  side  of  retina 
cross  in  optic  chiasma  and  pass  to  pulvinar  of  thalamus  of  opposite  side.  Macular 
fibres  are  partly  crossed  and  partly  uncrossed. 

Neurotic  No.  3. — ^a,  Axones  of  cells  in  pulvinar  to  cortex  of  occipital  lobe  of  cerebrum 
(this  connection  is  disputed) ;  3  b,  axones  of  cells  in  external  geniculate  body  to  cortex  of 
occipital  lobe  of  cerebrum;  3  a  and  36  constitute  the  primary  optic  radiation;  3  c,  s  d  and 
3  e,  axones  of  cells  in  deep  (fourth)  layer  of  superior  coUiculus  (see  p.  522)  decussate 
ventral  to  medial  longitudinal  fasciculus  (dorsal  tegmental  decussation  or  decussa- 
tion of  Meynert)  and  form  the  tractus  coUiculo-bulbaris  et  spinalis  or  predorsal 
bundle.  (Tr.  tectobulb.  el  spin.)  to  bulb  (medulla)  and  anterior  column  of  cord,  inner- 
vating by  coUaterals  and  terminals,  directly  or  indirectly,  chiefly  the  nuclei  of  III,  IV, 
VI,  and  VII  cranial  nerves  and  motor  nuclei  of  spinal  nerves.  3  /  and  3  g  (possibly 
another  neurone  intercalated  between  these  and  optic  terminals),  axones  of  cells  in  inter- 
stitial nucleus  of  Cajal  (Nu.  fasc.  long,  post.)  form  part  of  medial  longitudinal  fasciculus 
and  descend  on  same  side  to  anterior  column  of  cord  next  to  anterior  median  fissure, 
innervating  nuclei  of  III,  IV,  and  VI  cranial  nerves  and  motor  nuclei  of  spinal  nerves. 

Neurone  No.  4. — Axones  of  cells  in  above-mentioned  motor  nuclei.  Axones  from 
cells  in  median  nucleus  of  nerve  III  (Nu.  med.  N.  Ill)  and  possibly  in  Edinger-Westphal 
nucleus,  probably  innervate  the  intrinsic  muscle  of  eyeball  (ciliary  and  pupillary  reflex 
path). 

PaUio-tectal  fibres,  by  means  of  which  the  coUicular  reflex  centre  is  brought  under 
the  control  of  the  cerebral  cortex,  are  not  indicated. 

It  is  evident  from  the  diagram  that  the  cerebral  pathway  of  the  optic  nerve  is  via  the 
external  geniculate  body  (and  pulvinar  of  thalamus?),  and  the  reflex  pathway  is  via  the 
superior  colliculu  s. 


34 


530  THE  ORGANS 

now  lost  in  the  ventre- lateral  thalamic  nuclei,  cells  of  which  constitute  the  tertiary 
neurones  of  the  various  afferent  pallial  paths  (see  pp.  523  and  524). 

Intersegmental  Neurones. — The  cephalic  end  of  the  nucleus  ruber  is  still 
present  on  the  right  {Ntg).  On  the  left  are  seen  some  fibres  in  its  place,  lateral 
to  which  are  two  transverse  bundles  enclosing  a  strip  of  gray  matter.  These  are 
known  as  the  area  tegmenti  or  field  of  Forel  and  represent  a  subthalamic  forward 
extension  of  the  tegmentum.  The  gray  or  zona  incerta  may  be  regarded  as 
representing  a  continuation  of  part  of  the  reticular  formation.  The  ventral 
bundle  of  fibres  {HII)  are  probably  fibres  from  the  nucleus  lenticularis  {glp  and 
Pu,  right)  passing  through  the  pes  (or  rather  through  the  posterior  part  of  its 
continuation — the  internal  capsule)  as  perforating  fibres  {fp  on  right)  to  the 
corpus  subthalamicum  {Csth,  left)  and  other  subthalamic  regions,  possibly  also 
to  the  nucleus  ruber.  Some  of  these  fibres  are  collaterals  of  pes  fibres  and  may 
consequently  come  directly  from  the  pallium.  The  dorsal  bundle  {HI)  probably 
contains  fibres  connecting  red  nucleus  and  pallium.  Other  fibres  in  this  region 
are  probably  fibres  of  the  superior  cerebellar  peduncle  which  have  passed  by 
the  nucleus  ruber  to  the  lateral  nucleus  and  median  center  of  the  thalamus 
(see  also  p.  523)  and  possibly  also  fibres  of  the  secondary  trigeminal  tract. 
The  nucleus  of  the  medial  longitudinal  fasciculus  falls  in  the  level  between  this 
and  the  preceding  section.  In  general  it  seems  probable  that  portions  of  the 
corpus  striatum,  the  corpus  subthalamicum  and  certain  other  subthalamic 
nuclei,  the  substantia  nigra  and  part  of  the  nucleus  ruber  represent  certain 
phylogenetically  old,  rather  obscure,  efferent  forebrain  paths. 

Efferent  Suprasegmental  Neurones. — The  pes  pedunculi  now  lies  partly 
between  the  thalamus  and  nucleus  lenticularis  (see  p.  533)  constituting  the 
greater  part  of  the  internal  capsule.  The  parts  of  the  internal  capsule  as  shown 
in  horizontal  sections  of  the  hemispheres  are  shown  in  Fig.  352.  The  most 
dorsal  part  is  here  passing  into  the  corona  radiata  (p.  533)  of  the  cerebral  hemi- 
spheres (not  included  in  the  section).  The  part  present  in  this  level  is  the  most 
posterior  part  of  the  capsule  (occipito-temporal  pallio-pontile  fibres  (see  p.  533). 

Dorsal  to  the  mesial  part  of  the  pes  is  the  corpus  subthalamicum  which  has 
replaced  the  substantia  nigra.  It  receives  collaterals  from  the  pes  and  is  said 
to  contribute  fibres  to  the  latter.  It  also  appears  to  be  connected  by  fibres  with 
the  nucleus  lenticularis  (see  above).  Superior  cerebellar  peduncle  (see  Inter- 
segmental Neurones  above). 

Thalamus. — At  this  level  the  ventro-lateral  nucleus,  the  nucleus  arcuatus,  and 
the  median  center  of  Luys  can  usually  be  distinguished.  At  the  outer  border  of 
the  thalamus,  fibres  accumulate  forming  the  lateral  medullary  lamina.  These 
fibres  continue  outward  as  thalamic  radiations,  entering  the  internal  capsule 
which  they  may  follow  a  distance,  or  cross  obliquely  and  enter  the  corona 
radiata. 

Epithalamic  and  Hypothalamic  Structures  and  their  Connections. — The 
ganglia  habenulce  are  two  small  masses  of  gray  matter  occupying  eminences  on 
the  mesial  walls  of  the  thalamus.  A  bundle  of  fibres  near  each  is  the  stria  medul- 
laris  (near  the  tcenia  thalami)  consisting  of  fibres  from  the  olfactory  bulb  and 
trigonum  and  representing  afferent  olfactory  connections  (p.  532).  The  ganglion 
habenulse  contains  a  mesial  small-celled  and  a  lateral  large-celled  nucleus.     Their 


THE  XERVOUS  SYSTEM 


531 


axones  form  ihe  fasciculus  retroflexus  of  Meynert  to  the  interpeduncular  ganglion 
situated  more  caudally  (Fig.  351).  There  is  also  a  commissura  habcnulari's 
connectmg  the  two  ganglia.  The  stria  terminalis  (stria  cornea),  another  olfactory 
connection,  lies  in  the  groove  between  the  ventricular  surfaces  of  nucleus 
caudatus  and  thalamus.  The  tuber  cinereum  is  seen  projecting  ventrally 
Dorsal  to  this  are  seen  the  corpora  mammillaria  containing  lateral  and  mesial 
nuclei.  The  mammiUary  body  receives  some  fibres  of  the  fornix  (from  the 
rhinopalhal  cortex,  see  below)  and  also  fibres  from  the  medial  fillet  and  other 


Fig.  ^35'.— i>iaKram  of  Olfactory  Paths  (von  Bcchtercvv.j  A',  Root  fibres  of  vacus- 
^a,  commissura  anlerior;  cm,  corpus  mammillare;  cp,  fibres  fn,m  nucleus  halenurt^ 
postenor  comm,ssure;/6-,  tract  from  corpus  mammillare  to  (uuiden's  nucLs  j  "  Scu- 
us  mammillo-thalamicLis;  y/,  fasciculus  lonKitudinalis  medialis;/;-,  fornix  //f,  res  of 
o  n.x  loHKUs; ;;/;  nu.leus  habcnuhe;  ,/,  Kan^lion  intcrpcduncularc  A'A,  Kyr  is  wri  ormis 
i'J  r?'"'  'ned.al.s  ,«  fibres  from  (;,Kiden's  nucleus  lo  substai  ia  rc^ticul  SS 
na   nucleus  anterior  thalam.;  nG,  (iuddcn's  nucleus;  ;,/,  nucleus  icKmenti  {v    (  ud  IcnV 

^n:::^:^^::^  "Tk"''-';'  ^"''■'  "T'--"'-  -n>oris  mamminaris  from  lillct;  ^  ! 
corpora  quadrij,'emma;  r,  fibres  from  nucleus  IcKmenti  (v.  (uhKIcii)  lo  nuclei  of  cr'  n  -d 
nerves;  re,  radix  lateralis  tractus  olfaclorii;  ./,  fibres  of\ractus  olfiior  ,      i«oi     m 

torius  i  Un!  .h  '  '"■'  """'f  "f.^T"""!  olfactorium;  //,,  ihalanuis;  /;-.,  tniclus  olfac- 
lorius,  «,  ticnia  Ihalami;  x,  fasciculus  retroflexus. 


532  THE  ORGANS 

ascending  tracts  in  the  reticular  formation.  It  gives  rise  to  the  bundle  of 
Vicq  d'Azyr  (mammillo-thalamic  tract)  to  the  dorsal  nucleus  of  the  thalamus, 
and  mammillo-tegmental  fibres  to  the  nucleus  of  Gudden  (Fig.  351)  and  red 
nucleus.  The  fibres  entering  the  mammillary  body  from  the  fillet  and  other 
ascending  tracts,  together  with  the  mammillo-tegmental  tract,  constitute  its 
peduncle.  It  is  not  improbable  that  the  mammillary  body  is  a  link  in  the 
afferent  gustatory  path  (p.  476,  II).     (See  also  Endbrain.) 

On  the  right  is  seen  the  posterior  part  of  the  nucleus  lenticularis  of  the  corpus 
striatum. 

The  Endbrain  or  Telencephalon. 

The  endbrain  consists  of  pallium  (dorsal  expanded  part),  corpus 
striatum,  and  rhinencephalon.  Two  principal  parts  of  the  pallium 
may  be  distinguished;  the  olfactory  palhum  or  rhinopallium  (archi- 
pallium),  including  principally  the  cornu  ammonis  and  gyrus  denta- 
tus;  and  the  neopallium  including  the  greater  part  of  the  cerebral 
hemispheres. 

The  rhinencephalon^  includes  the  olfactory  nerves  and  bulb,  the 
trigonum  olfactorium,  the  tuberculum  olf actorium  or  anterior  perfor- 
ated space,  and  the  gyrus  hippocampi,  in  part  at  least  (pyriform  lobe). 
The  olfactory  nerve  is  composed  of  axones  of  cells  in  the  olfactory 
mucous  membrane  which  terminate  in  the  olfactory  bulb.  They  there 
form  synapses  with  the  dendrites  of  the  mitral  cells,  the  axones  of 
which  constitute  the  secondary  tract,  part  of  which  decussates  in 
the  pars  olfactoria  of  the  anterior  cerebral  commissure.  A  secondary 
tract  ("lateral  root")  proceeds,  with  tertiary  tracts,  to  the  cortex  of 
the  gyrus  hippocampi  and  thence  to  the  cornu  ammonis.  Efferent 
axones  of  cornu  ammonis  cells  are  collected  in  the  fimbria  and  descend 
by  the  fornix  to  the  mammillary  body,  the  further  caudal  connec- 
tions of  which  have  been  described  (p.  531  j.  Fibres  of  the  fimbria 
also  cross,  forming  the  commissure  of  the  fornix  (olfactory  pallial 
commissure) .  Secondary  olfactory  tracts  also  pass  to  the  trigonum, 
whence  tertiary  neurones  pass  as  the  stria  medullaris  to  the  ganglion 
habenulae  (see  p.  530  and  Fig.  351).  The  principal  commissure 
of  the  rhinencephalon  is  the  anterior  cerebral  commissure. 

The  corpus  striatum  consists  of  the  nucleus  caudatus  and  nucleus 
lenticularis,  the  connections  and  significance  of  which  are  obscure. 
They  receive  collaterals  from  the  descending  pallial  fibres  which 
pass  by  them  and  also  apparently  send  out  fibres  to  join  the  latter. 
They  also  have  connections  with  rhinencephalon  and  thalamus. 

1  The  term  rhinencephalon  is  often  used  to  include  also  the  olfactory  pallium. 


THE  NERVOUS  SYSTEM 


533 


The  pallium  consists  of  an  extensive  external  convoluted  sheet 
of  gray  matter  {cortex  pallii  or  cortex  cerebri)  and  of  white  matter 
underlying  the  gray.  In  the  white  matter  may  be  distinguished 
the  corona  radiata  composed  of  the  afferent  and  efferent  pallial 
fibres  connecting  the  pallium  mth  other  parts  of  the  brain  {projec- 
tion fibres).  The  remaining  fibres  of  the 
white  matter  are  association  fibres  of  the 
pallium  and  are  either  crossed  or  com- 
missural, connecting  the  two  hemispheres 
{corpus  callosum  and  fornix  commissure), 
or  are  uncrossed.  The  term  association 
fibres  is  often  restricted  to  the  uncrossed 
fibres. 

The  aft'erent  connections  of  the  neopal- 
lium (p.  523)  and  rhinopallium  (p.  532) 
have  been  summarized  and  also  the  efferent 
connections  of  the  rhinopallium  (p.  532). 

The  following  are  the  principal  descend- 
ing or  efferent  connections  of  the  neopallium: 
(i)  The  pyramidal  or  pallio-spinal  tract. 
This  is  composed  of  the  axones  of  the  giant 
cells  (of  Betz)  of  the  arm,  body,  and  legpre- 
central  motor  areas.  They  descend  in  the 
corona  radiata,  the  posterior  limb  of  the 
internal  capsule,  middle  part  of  the  pes, 
and  thence  through  pons  and  medulla  to 
the  cord.  Their  decussation  and  further 
course  has  been  described.  (2)  The  de- 
scending tracts  to  the  motor  nuclei  of  the 
cranial  nerves  originate  from  precentral  cells 
of  the  various  areas  controlling  the  muscles 
in  question  and  pass  down  in  the  vicinity 
of  the  genu  of  the  internal  capsule.  Their 
path  is  not  so  well  known  but  they  appar- 
ently do  not  pass  down  in  the  pes  through- 
out their  course  (pp.  524,  521,  etc.).  (3) 
The  pallio-pontile  system  to  the  j)ons  (continuation  to  opposite 
cerebellar  hemisi)here).  This  originates  in  various  parts  of  the 
cortex.  The  fibres  from  the  occipital  (?)  and  temporal  regions  pass 
down  in  the  extreme  posterior  part  of  the  internal  capsule  and  lateral 


Fig.  352. — Scheme  of 
General  Arrangement  of 
fibres  in  Internal  Capsule, 
(von  Bechterew.)  /,  //, 
///,  The  three  parts  of  the 
lenticular  nucleus;  nc,  nu- 
cleus caudatus;^/;, thalamus; 
gp,  globus  pallidus;  pt,  put- 
amen;  i,  fibres  of  anterior 
thalamic  ])cduncle;  2,  fibres 
of  medial  (frontal)  pons 
system  (frontal  paUio-pon- 
tile  fibres);  3,  efferent  pal- 
lial fibres  to  motor  nuclei  of 
cranial  nerves;  4,  pyramidal 
fibres  (efferent  pallial  fibres 
to  motor  nuclei  of  spinal 
nerves);  5,  pyramidal  fibres 
mingled  with  those  of  the 
afferent  (sensory)  path;  6, 
fibres  of  the  lateral  jions 
system  (occipilio-temporal 
palUo-pontilc  fibres).  The 
various  systems  arc  not 
sharply  marked  off  as  indi- 
cated, but  are  more  or  less 
intermingled. 


534 


THE  ORGANS 


PiTh 

Coa  X  Vli  ti  Rop  Fli 
Fig.  353. — Transverse  Section  through  the  Cerebral  Hemispheres,  Corpora  Striata 
and  Thalamus.  Weigert  preparation.  (Dejerine.)  II,  Tractus  opticus;  Alent,  ansa 
lenticularis;  c,  sulcus  centralis  (Rolandicus) ;  Ca,  gyrus  centralis  anterior;  Cell,  corpus 
caUosum;  Ce,  capsula  externa;  CFo,  columna  fornicis;  Cia,  crus  anterior  capsul.  int.; 
Cig,  genu  capsul.  int.;  CI,  claustrum;  dim,  sulcus  callosomarginalis;  Cng,  cingulum; 
Coa,  commissura  anterior;  Cp,  gyrus  centralis  posterior  (ascending  parietal  convolution) ; 
CR,  corona  radiata;  Far,  fasciculus  arcuatus;  Fli,  fasciculus  longitudinalis  inferior; 
Frn,  gyrus  fornicatus;  fs,  sulcus  frontalis  superior;  Fs,  gyrus  frontalis  superior;  Fu, 
fasciculus  uncinatus;  Fus,  gyrus  fusiformis;  glp,  globus  pallidus  (inner  segment);  glp' , 
globus  pallidus  (outer  segment);  I,  insula;  Ime,  lamina  m.edullaris  externa  nuclei  lentic- 
ularis;  Ime' ,  supplementary  lamina  of  the  outer  segment  of  the  globus  paUidus;  Imi, 


THE  NERVOUS  SYSTEM  535 

part  of  the  pes,  those  from  the  frontal  region  pass  down  in  the  anterior 
Hmb  of  the  internal  capsule  and  mesial  part  of  the  pes.  (4)  Pallio- 
tectal  fibres  to  the  midbrain  roof.  (5)  Fibres  to  the  substantia 
nigra  and  corpus  subthalamicum.  (6)  Fibres  to  the  red  nucleus. 
(7)  Pallio-thalamic  fibres  (see  p.  523).  (8)  Fibres,  or  collaterals, 
to  the  corpora  striata.     (Fig.  352.) 

The  crossed  association  fibres  of  the  neopallium  (corpus  callosum) 
connect  principally  corresponding  parts  of  the  hemispheres.  The 
long  uncrossed  association  fibres  (furthest  from  the  gray  matter) 
form  certain  more  or  less  well-defined  bundles  among  which  are  the 
following:  (i)  The  cingulum,  a  longitudinal  bundle  near  the  corpus 
callosum;  also  contains  projection  fibres  and  belongs  to  the  olfactory 
part  of  the  brain  as  well  as  to  the  neopallium.  (2)  The  superior 
longitudinal  fasciculus  or  fasciculus  arcuatus;  connects  frontal  with 
occipital  and  part  of  temporal  lobes.  (3)  The  inferior  longitudinal 
bundle  connecting  temporal  and  occipital  lobes.  It  may,  however, 
be  a  projection  bundle.  (4)  The  uncinate  fasciculus  connecting 
frontal  and  temporal  lobes.  (5)  The  perpendicular  fasciculus  of 
Wernicke  connecting  inferior  parietal  and  fusiform  lobules.  Pro- 
jection fibres  may  form  portions  of  these  bundles. 

Besides  the  above  long  association  fibres  there  are  shorter 
association  fibres  nearer  the  gray  matter  which  connect  adjoining 
convolutions  (fibrae  propriee  of  Meynert). 

PRACTICAL  STUDY 

1.3.  Transverse  Section  through  the  Cerebral  Hemispheres,  Corpora  Striata 
and  Thalamus     (Fig.  353) 

First  distinguish  in  general  (i)  the  pallium,  its  cortex  and  white  matter,  (2) 
the  corpus  slrialum  and  its  divisions,  i.e.,  the  caudate  nucleus  and  the  lenticular 
nucleus,  the  latter  being  subdivided  into  the  pulamen  and  f!,Iol)us  pallidus  and 
(3)  the  thalamus  and  other  structures  of  the  interbrain. 

lamina  mcdullaris  interna  nuclei  lenticularis;  mp  and  nis,  sulcus  tircularis  (Reili);  NA, 
nucleus  amy^flaliformis;  A'c,  nucleus  caudalus;  OjiR,  ()[)crculum;  oti,  sulcus  occijjitotcm- 
poralis  inferior;  pCK,  pes  coronx'  rarliata;;  I'iTh,  jjcdunculus  inferior  thalami;  prs, 
sulcus  prajccntralis;  ]'u,  putamen;  rcc,  stratum  reticulum  coronie  radiatac;7?(>/',  radiatio 
optica;  .V,  fissura  Sylvii  (jio.-.tcrior  hranchj;  Sgc,  substantia  ^risca  centralis;  sM,  sulcus 
Monro!;  Sge,  substantia  grisea  subei)en(lymalis;  ssc,  stratum  subcallosum:  SLrz,  stratum 
zonalc  thalami;  Tbc,  tuber  cinercum;  Th,  thalamus  o[)ticus;  ti,  sulcus  temporalis  in- 
ferior; Ti,  gyrus  temporalis  inferior;  Im,  sulcus  temporalis  mcdius;  Tm,  gyrus  temi)oralis 
mcdius;  Is,  sulcus  tcm|)oralis  superior;  Ts,  gyrus  temporalis  superior;  Tic,  taenia  tccta; 
U ,  uncus;  VI,  ventriculus  lateralis;  Vti,  ventriculus  lateralis  (cornu  inferius);  vsl, 
}>edunculus  anterior  thalami;  -Y,  |)edunculus  putaminis;  CM,  Commissure  of  Meynert. 


536  THE  ORGANS 

Afferent  Roots,  their  Terminal  Nuclei,  Secondary  Tracts,  and  Tertiary 
Neurones. — The  optic  tract  here  forms  a  part  of  the  ventral  surface  of  the  brain. 
The  geniculo-cortical  portion  of  the  optic  path  forming  a  part  of  the  optic 
radiation  may  be  seen.  Other  afferent  pallial  connections  are  hardly  distin- 
guishable among  the  fibres  connecting  thalamus  and  pallium. 

Efferent  Suprasegmental  Neurones, — A  great  part  of  the  pes  has  now  entered 
the  corona  radiata.  The  part  now  about  to  enter  the  corona  is  the  anterior  limb 
of  the  internal  capsule  (Fig.  352).  The  ansa  lenticularis  is,  according  to  some 
authorities,  composed  of  fibres  or  collaterals  from  the  pes  to  the  lenticular  nucleus. 
The  fibres  of  the  anterior  peduncle  of  the  thalamus  are  evident.  They  are  con- 
sidered by  some  as  composed  of  cortico-thalamic  fibres.  The  anterior  pillars  of 
the  fornix  (efferent  rhinopallial)  are  shown  cut  through  twice,  the  upper  section 
shows  its  earlier  course  emerging  from  the  fimbria,  the  lower  section  is  near  its 
termination  in  the  mammillary  body. 

For  other  structures  of  thalamus,  epithalamus,  and  hypothalamus  see  Fig. 

353- 

The  Pallium. — In  the  white  matter  distinguish  as  far  as  possible  the  corona 
radiata,  the  corpus  callosum,  and  the  long  association  bundles  {inferior  longitudinal 
fasciculus,  fasciculus  uncinatus,  a.nd fasciculus  arctiattis)  (seep.  535).  Note  the 
nucleus  amy gdaliformis ,  the  anterior  perforated  space  and  the  anterior  commissure, 
belonging  to  the  rhinencephalon. 

Other  details  shown  in  Fig.  353  should  be  studied. 

The  Cerebral  Cortex. — The  following  types  of  cells  are  found  in 
the  cerebral  cortex:  (i)  Pyramidal  cells.  This  is  the  prevaihng 
type  and  is  characterized  by  a  long  apical  dendrite  usually  directed 
toward  the  surface  of  the  brain.  This  dendrite  gives  off  branches, 
and  usually  reaches  the  outer  cortical  layer,  there  to  break  up  into  a 
number  of  branches.  From  the  cell  body  are  also  given  off  a  number 
of  basal  dendrites.  By  the  Golgi  and  EhrHch  methods,  gemmules 
can  be  demonstrated  on  the  dendrites.  The  axone  proceeds  from  the 
base  of  the  cell  (opposite  to  the  apical  dendrite)  and  usually  passes 
into  the  white  matter.  It  gives  off  several  collaterals  on  its  way  to 
the  white  matter.  (2)  Stellate  cells.  These  have  dendrites  passing 
in  various  directions.  Many,  especially  the  smaller  (granules),  may 
have  short  axones  (Golgi's  second  type).  (3)  Polymorphous  cells  of 
a  triangular  or  spindle  shape  are  usually  found  in  the  deepest  layers  of 
the  cortex  and  send  their  axones  into  the  white  matter.  (4)  Hori- 
zontal cells  (of  Cajal),  found  in  the  outer  layer,  with  long  horizontal 
dendrites  and  axones  confined  to  the  outer  layer.  (5)  Inverted 
pyramidal  cells  (of  Martinotti)  with  axones  directed  toward  the 
surface.     (Fig.  355.) 

The  largest  cells  of  the  cortex  (giant  cells  of  Betz)  are  very  rich  in 
chromophilic  substance  arranged  similarly  to  that  in  the  efferent 


THE  NERVOUS  SYSTEM 


537 


root  cells  of  cord  and  brain.  The  medium  and  small  cells  have 
fewer  chromophilic  bodies  which  are  often  in  the  shape  of  irregular 
masses,  either  near  the  periphery  of  the  cell  or  around  the  nucleus. 
The  neurofibrils  vary  in  their  arrangement  according  to  the  shape  of 
the  cell. 


.'.■V   -V^;,!-  ;i.N-'«-ll  lit '7/ a.'  --1 


.';*  '■..'■'■A' 


.\'  r-v  -f 


i.  I  • 


Fig.  354. — Vertical  Sections  of  Calcarine  Area  of  Adult  Human  Cortex.  Left, 
Weigcrt  preparation  sfiowing  fibre  arrangement.  Right,  Arrangement  of  Cells. 
(Cami>bell.)  6",  Line  ol  Gennari;  K,  radiary  layer;  S,  supraradiary  layer;  Z,  Layer  of 
superficial  tangential  filjres  in  molecular  layer;  i,  molecular  laj^er;  2,  external  granular 
(small  |>yramidj  layer;  3,  j)yramid  layer;  4,  (large  granules)  and  5  (small  granules), 
internal  granular  layer;  C,  ganglionic  layer  (containing  solitary  cells  of  Meynert);  7, 
multiform  layer. 

'I'ho  neuroglia  cells  and  fibres  are  in  general  similar  to  those  in 
other  parts  of  the  nervous  system. 

The  cells  of  the  cortex  are  arranged  in  layers  which  have  the  same 
general  character  throughout,  but  in  various  regions  exhibit  variations 


538 


THE  ORGANS 


II 


such  as  suppression,  diminu- 
tion, enlargement,  or  subdi- 
vision of  certain  layers.  The 
cell  layers  of  the  cortex  are: 
(i)  Molecular  layer  (zonal 
layer,  plexiform  layer  of 
Cajal).  This  contains  the 
horizontal  cells,  other  cells 
with  short  axones,  and  also 
receives  the  axones  of  the 
Martinotti  cells.  Besides 
this,  it  contains  the  terminal 
branches  of  the  apical  den- 


Fig-  355- 


Fig.  355. — Vertical  section  of 
Calcarine  Area  of  Cortex  of  an  In- 
fant 15-20  days  old.  (Cajal,  com- 
bined from  three,  /,  II  and  ///, 
somewhat  overlapping  figures.  The 
multiform  layer  is  not  included). 
Golgi's  method. 

/. — A,  Molecular  layer;  B,  ex- 
ternal granular  layer  (of  small  pyra- 
mids); C,  pyramidal  layer  (of  me- 
dium pyramids);  a,  descending  ax- 
ones; h,  ascending  collaterals;  c, 
apical  dendrites  of  large  pyramidal 
cells  in  ganglionic  layer. 

//.• — A ,  Sublayer  of  large  stellate 
cells;  B,  sublayer  of  small  stellate 
cells;  C,  outer  part  of  ganglionic 
layer;  a,  crescentic  stellate  cells;  b, 
and  /,  horizontal,  spindle-shaped 
stellate  cells;  c,  medium-sized  pyram- 
idal cells;  e,  stellate  cells  with 
arched  axones;  g,  triangular  stellate 
cells  with  stout,  arched  collaterals; 
//,  pyramidal  cells  with  arched  axones. 
///. — A,  Part  of  internal  granu- 
lar layer;  B,  sublayer  of  small  pyram- 
idal cells  with  arched  ascending 
axones;  C,  sublayer  of  large  pyra- 
mids; a,  large  pyramidal  cell;  b, 
g  medium-sized  pyramidal  cell  with 
2  long  descending  axone;  c,  small  pyr- 
gi  amidal  cell  with  arched  ascending 
^  axone;  d,  pyramidal  cell  with  axone 
split  into  two  arched  ascending 
branches;  e,  pyramidal  cells  whose 
axone  sends  out  various  ascending 
branches;  f,g,h,  stellate  cells  with  as- 
cending axones  which  branch  in  B 
and  in  the  sublayer  of  small  stel- 
late cells;  i,j,k,  pyramidal  cells  with 
arched  ascending  axones  which  send 
branches  into  the  ganglionic  layer. 


THE  NERVOUS  SYSTEM  539 

drites  of  the  pyramidal  cells.  (2)  External  granular  layer,  very 
often  termed  the  layer  of  small  pyramids.  The  dendrites  of  the 
cells  of  this  layer  mostly  enter  the  first  layer,  their  axones  pass 
downward  into  the  white  matter.  (3)  Pyramidal  layer,  often  called 
the  layer  of  superficial  medium  and  large  pyramids.  This  is  com- 
posed principally  of  typical  pyramids  sending  dendritic  branches 
into  the  first  layer  and  axones  into  the  white  matter.  The  larger 
cells  are  in  the  deeper  part  (sublayer  of  large  pyramids).  This  layer 
also  contains  many  granule  cells  with  short  axones  and  cells  of  Marti- 
notti,  (4)  Internal  granular  layer.  Here  the  predominating  elements 
are  stellate  cells,  the  larger  usually  sending  their  axones  into  the 
white  matter.  Among  these  are  many  short  axone  granules,  the 
axones  of  which  end  in  the  same  layer  or  in  more  superficial  layers. 
(5)  Ganglionic  layer  or  deep  layer  of  large  and  medium  sized  pyramids. 
These  send  their  axones  into  the  white  matter.  Mingled  with  them 
are  short  axone  and  Martinotti  cells.  (6)  Multiform  layer  or  layer 
of  polymorphous  cells.  These  usually  send  their  axones  into  the 
white  matter.  Mingled  with  them  are  short  axone  and  Martinotti 
cells.     (Figs.  354,  355  and  356.) 

The  cells  of  the  cortex  obviously  fall  into  two  classes:  efferent  pro- 
jection cells  and  association  cells.  Which  cells  are  projection  cells  is 
not  definitely  known,  except  in  the  case  of  the  precentral  motor  cor- 
tex where  it  has  been  established  that  these  cells  are  the  cells  of  Betz, 
the  axones  of  which  form  the  pyramidal  tract  and  the  fibres  to 
motor  cranial  nerve  nuclei.  An  examination  of  this  area  shows  that 
the  association  cells  must  enormously  outnumber  the  efferent  pro- 
jection cells  in  the  cortex.  The  association  cells  comprise  the  short 
axone  cells  and  cells  the  fibres  of  which  enter  the  white  matter,  but 
terminate  in  some  other  part  of  the  cortex,  forming  the  association 
fibres  of  the  white  matter.     (Compare  p.  533.) 

It  is  thus  evident  that  every  part  of  the  cortex  contains  termina- 
tions of  association  fibres.  The  areas  containing  the  terminations 
of  afferent  projection  fibres  are  those  which  receive  the  thalamocorti- 
cal continuations  of  the  afferent  pallial  paths  and  the  continuations 
of  the  olfactory  paths.  From  observations  made  with  the  Golgi 
method  it  seems  probable  that  the  afferent  projection  fibres  arc 
coarse  fibres  which  may  ramify  throughout  the  greater  part  of  the 
thickness  of  the  cortex,  but  are  confined  mainly  to  the  third  and 
fourth  layers.  The  principal  areas  of  the  cortex  receiving  the  af- 
ferent projection  fibres  are  the  hippocampal  area  (olfactory),  the  cal- 


THE  ORGANS 


.1.    i 


^r^l-:-, 


i^  h  ':  ■ 


,^i-:. 


i  i 


>i  ;  •  -  ■ 


]5    v\:  V 


v.-    /. 


■r  ii 


i 


Itt! 


f  iJ^l^i 


r\  i^-'^'^ 


''■'A  » 


i>i/  i^- > 


^    i' 


.•>:v 


« 

:;-^ 


Fig.  3 s6.— Vertical  Sections  of  Precentral  or  Motor  Area  of  Adult  Human  Cortex. 
Left  Weigert  preparation  showing  fibre  arrangement.  Right,  Arrangement  of  cells. 
(Campbell.)  B,  Position  of  line  of  Baillarger,  its  position  obscured  by  surrounding 
wealth  of  fibres;  R,  radiary  layer;  S,  supraradiary  layer;  Z,  layer  of  superficial  tangential 
fibres  in  molecular  layer,  dense  and  weU  defined;  i,  molecular  layer;  2,  external  granular 
layer  (small  pyramids),  3  (medium-sized)  and  4  (large),  pyramid  layer;  s,  mternal 
granular  layer,  indistinct  and  with  scattered  granule  or  stellate  cells;  6,  ganglionic  layer 
(large  deep  pyramids);  7,  multiform  layer. 


THE  NERVOUS  SY§TE:M  541 

carine  area  (visual,  fibres  from  lateral  geniculate  body),  the  trans- 
verse temporal  gyri  of  Heschl  (auditory,  fibres  from  medial  geniculate 
body),  and  the  pre-  and  postcentral  areas  (postcentral  only,  according 
to  some  authorities,  area  of  general  sensation  from  body  and  head, 
fibres  from  ventrolateral  thalamic  nuclei).     (Fig.  357.) 

The  medullated  fibres  of  the  cortex  consist  of  radially,  obliquely, 
and  tangentially  running  fibres.  The  radial  fibres  enter  the  cortex 
from  the  white  matter  in  bundles  known  as  the  radiations  oj  Meynert 
which  extend  a  variable  distance  toward  the  periphery,  diminishing 
until  they  end  usually  in  the  third  layer.  They  consist  mainly  of  the 
axones  of  the  adjoining  cells  passing  to  the  white  matter.  Their 
fibres  are  of  varying  calibre,  the  coarsest  originating  from  the  largest 
cells.  The  oblique  fibres  form  a  dense  plexus  of  coarse  and  fine  fibres 
between  the  radial  fibres,  the  interradiary  plexus.  Toward  the 
surface  fin  the  second  and  third  cell  layers)  they  form  a  delicate  plexus 
of  fine  fibres.  This  latter  plexus  lies  principally  superficial  to  the 
radiations  of  Meynert  and  is  the  supraradiary  plexus.  A  denser 
aggregation  of  irregular  fibres  constitute  the  line  or  stria  of  Baillarger 
located  in  the  layer  of  superficial  large  pyramids.  It  is  probable  that 
this  represents  a  layer  especially  rich  in  terminals  of  fibres  from  the 
white  matter.  Other  stria?  are  also  described.  Besides  represent- 
ing the  terminals  of  fibres  from  the  white  matter  the  oblique  fibres 
in  general  are  also  composed  of  medullated  collaterals  of  axones  of 
pyramids  and  possibly  arborizations  of  short  axone  cells.  A  few 
coarser  fibres  ascending  to  the  molecular  layer  are  ascending  fibres 
from  Martinotti  cells.  The  deep  tangential  fibres,  most  marked  on 
the  sides  of  the  convolutions  and  in  the  sulci,  are  considered  short 
association  fibres  belonging  to  the  fibrae  propria)  of  Meynert.  In 
the  molecular  layer  are  the  superficial  tangential  fibres  consisting  of 
the  axones  of  the  horizontal  cells  and  the  terminals  of  the  axones 
of  Martinotti  cells.     (Figs.  354  and  356.) 

The  cortex  is  divided  into  various  areas  by  various  investigators, 
the  areas  being  distinguished  (a)  by  the  time  of  medullation  (myelo- 
genctic  method  of  Flcchsig),  (b)  by  the  number  and  arrangement  of 
the  medullated  fibres  (myeloarchitccture),  especially  the  number, 
thickness,  and  distinctness  of  the  stria),  such  as  that  of  Baillarger, 
formed  by  them,  and  (c)  by  the  number  and  arrangement  of  the  cells 
(cytoarchitecture).  Many  such  areas  have  been  thus  distinguished 
by  different  investigators  with  results  agreeing  in  many  respects  but 
differing  in  others.     The  areas  rrk)st  clearly  defined  and  concerning 


542 


THE  ORGANS 


^irO>  Precenhal        fos^'* 


yisM-psj/chiB 


^udito-sensoru 


XertiT" 


eensory 


II 

Fig.  357. — Diagram  (orthogonal)  showing  Cortical  Areas  as  determined  by  the 
Arrangement  and  Distribution  of  Fibres  and  Cells  (A.  W.  Campbell).  Large  portions 
of  important  areas  are  concealed  within  fissures,  e.g.,  the  calcarine  or  visual  {visuo-sen- 
sory,  within  the  calcarine  fissure)  precentral  (motor)  and  postcentral  (within  the  fissure  of 
Rolando)  and  especially  the  acoustic  (audito-sensory)  which  is  almost  completely  hidden 
within  the  Sylvian  fissure.     A,  B  and  C,  parts  of  the  limbic  lobe. 


THE  NERVOUS  SYSTEM  543 

which  there  is  perhaps  the  most  general  agreement  are  the  vari- 
ous sensory  (afferent  projection)  areas  already  enumerated  (p.  539) 
and  the  motor  (efferent  projection)  precentral  area  (Fig.  357).  These 
areas  myelinate  first  (at  or  soon  after  birth),  next  areas  adjacent  to 
them,  and  last  areas  occupying  a  considerable  portion  of  the  human 
pallium  but  much  less  extensive  in  other  mammals.  There  is 
much  diff'erence  of  opinion  as  to  the  extent  to  which  these  last 
myelinating  areas  are  supplied  mth  projection  fibres.  According 
to  some  authorities  the  areas  myelinating  last  have  no  projection 
fibres  and  are  consequently  entirely  composed  of  association  cells 
and  fibres.  Perhaps  the  two  best-marked  of  the  various  areas  are 
the  motor  and  visual  areas  the  structure  of  which  is  shown  in  figures 
354.'  355  s-^d  356.  The  motor  precentral  cortex  is  characterized  by 
the  presence  of  the  giant  cells  of  Betz,  by  an  almost  complete  absence 
of  an  internal  granular  layer  and  by  a  great  wealth  of  fibres.  The 
calcarine  or  visual  area  is  characterized  by  a  strongly  marked  line 
of  Gennari  (  =  Baillarger)  and  by  a  double  or  triple  internal  granular 
layer  containing  large  granules  in  place,  apparently,  of  the  superficial 
large  pyramids.  The  line  of  Gennari  is  probably  partly  composed 
of  the  terminals  of  the  fibres  of  the  optic  path  (geniculo-calcarine 
fibres). 

TECHNIC 

(i)  The  general  structure  of  the  cerebellum  is  well  brought  out  by  staining 
sections  of  formalin-Miiller's  fluid-fixed  material  with  hgematoxylin-picro-acid- 
fuchsin  (technic  3,  p.  21),  and  mounting  in  balsam. 

(2)  The  arrangement  of  the  cell  layers  of  both  cerebellum  and  cerebrum  as 
well  as  certain  details  of  internal  structure  of  the  cells,  can  be  studied  in  sections 
of  alcohol-  or  formalin-fixed  material  stained  by  the  method  of  Nissl  (technic, 
P-  38). 

(^.3)  'J'he  distribution  of  the  meduUated  nerve  fibres  of  either  the  cerebellar  or 
cerebral  cortex  is  best  demonstrated  by  fixing  material  in  jVIiiller's  fluid  (technic 
4,  p.  6)  or  in  formalin-Miiller's  fluid,  and  staining  rather  thick  sections  by  the 
Weigert  or  Weigert-Pal  method  (technic,  p.  :i^). 

(4)  The  external  morphology  of  the  cerebellar  and  cerebral  neurones  and  the 
relations  of  cell  and  fibre  can  be  thoroughly  understood  only  by  means  of  sec- 
tions stained  by  one  of  the  (iolgi  methods  (technic,  pp.  35  and  36).  Ksi)ecially 
in  the  case  of  the  cerebellum,  sections  should  be  made  both  at  right  angles,  and 
longitudinal  to  the  long  axis  of  the  convolution.  Golgi  preparations  from 
embryonic  material  and  fnjrn  the  brains  of  lower  animals  furnish  instructive 
pictures. 

C5)  'I'he  silver  method  of  ("ajal  shouUl  be  used    esj)ecially  with  alcohol  fixa- 


544  THE  ORGANS 

tion  (technic  p.  38,  No.  2),  both  for  the  neurofibrils  and  for  the  external  mor- 
phology of  the  neurones.     It  is  especially  successful  with  the  cerebellum. 
(6)  Neuroglia  stains  should  also  be  used. 

The  Pituitary  Body 

{See  page  407.) 

The  Pineal  Body 

The  pineal  body  originates  as  a  fold  of  the  wall  of  the  primary 
brain  vesicle.  It  lies  upon  the  dorsal  surface  of  the  inter-  and  mid- 
brain, being  connected  with  the  former.  The  pineal  body  is  appar- 
ently of  the  nature  of  a  rudimentary  sense  organ,  being  sometimes 
referred  to  as  the  median  or  pineal  eye.  In  man  it  is  surrounded 
by  a  firm  connective-tissue  capsule,  which  is  a  continuation  of  the  pia 
mater.  This  sends  trabeculse  into  the  organ,  which  anastomose  and 
divide  it  into  many  small  chambers.  The  latter  contain  tubules  or 
alveoli  lined  with  cuboidal  epithelium.  This  may  be  simple  or  strati- 
fied, and  frequently  almost  completely  fills  the  tubules.  Within  the 
tubules  are  often  found  calcareous  deposits  known  as  "brain  sand." 

TECHNIC 

The  general  structure  of  the  pituitary  body  and  of  the  pineal  body  can  be 
studied  by  fixing  material  in  formalin-Miiller's  fluid  (technic  5,  p.  7)  and  staining 
sections  with  haematoxylin-eosin  (technic  i,  p.  20). 

General   References   for   Further   Study 

Bailey  and  Miller:  A  Text-book  of  Embryology,  New  York,  1909.  Chaps. 
XVII  and  XVIII. 

Barker:  The  Nervous  System  and  its  Constituent  Neurones,  New  York, 
1899. 

Dejerine:     Anatomic  des  centres  nerveux,  Paris,  1895. 

Edinger  L. :  Vorlesungen  iiber  den  Bau  der  nervosen  Zentralorgane  des 
Menschen  und  der  Tiere,  Leipsig,  1908  and  191 1. 

Van  Gehuchten:  Anatomic  du  systeme  nerveux  de  I'homme,  Louvaine, 
1906. 

Golgi:  Untersuchungen  iiber  den  feineren  Bau  des  centralen  und  peripher- 
ischen  Nervensystems,  Jena,  1894. 

Johnston,  J.  B.:     The  Nervous  System  of  Veterbrates,  1906. 

KoUiker:     Handbuch  der  Gewebelehre  des  Menschen,  Leipsic,  1896. 

Von  Lenhossek:  Der  feinere  Bau  des  Nervensystems  im  Lichte  neuester 
Forschungen,  Berlin,  1895. 


v£-B  ■"    • 
'-'  U  a  c  c 

■^  ""  u 

>-   <U    C    K    >■ 


>—       .v  o 


«-    3-5°  ° 

g          O    S    «  M 

U        o  ^  ^  O 

u  o  t,  C  ft  ft 

f-     H     O  O 


tc 

n 

1, 

y: 

CO 

O 

3 

U 

eu 

:S  -"^ 

o  <u  S  2 

taS    .  ^; 

^.  --d-d 

'O'-l    M    Cj 

^>2o 


•2  -d      -o  c  >• 

i^  w  g  M  _  4) 

ft  o  ?  o  q  1-. 

2 ^ 


•  ■"  3  c 

o  > 

•:;!  o  1=  S 

2  1-.  n!  o 


M  nl  M  ca 

S.S  2  - 

o'p,  o> 
•  C  w  Ri-i 


.S     -M 


■52     ■«     .2 


a -^ 


.Sj- 


.    „•    «    Gj    0) 

3  cs  d  o  n  <u  aCQ 
2;    2:    ^    Z 


s       ^ 


i>  O  o 


3-ri 

>?«! 


5> 


is- 


p-i*  o  fe;s- 


(UJ3   C 

rt'^  S  o  C  ^, 
5-^J5  g    -  o 


-  o  c_  _    •  u 


"■"IS" 

c"o'S  P 


o  S  ^  ^-^ 
5  33-3  g) 


tn 

T3 

3 

XI 

0 

ft 

E 

0 

e  o  c 


■5_C 


"  M  °  nJ 

S    <; 


°:s   a^ 


c—      c 


O  0! 

—  c 

c  o 

a  u 
O 


£  E 


ii  " 

2 


<«  S 


.  c 

^J3 

3 

3 

M 

0 

2° 

iis 

(U-O 

bo 

M 

OT3 

u 

a 

a 

a 

0^ 

a 

cd 

^ 

2;B 

2 

0 

0 

.2 

a 

•    . 

^s 

<u 

0  3 

C 

a 

<g  (U 

v 

•*3X3 

u 

•0 

CI;; 

pt; 

<i 

rtta 

to 

<4 

<  > 

|i^  "    *    G  " 


35 


S  to  "^ 
cS  fi  g 


■a  H  4)  <u 
"^      o  " 

ci3  cd  (It  (-1 


Cli 


1^ 


O 


Oi      (H      S 


S  ftC 

^tSd^ 

ss'i 

^'w  ^ 

^  s 

-  3  O  m  R 
-d  o  h  3  &: 

■o  > . . 

apezoi 
lemnis 
ticse 
emnisc 
.y  kno 

pezo: 

oli 

ssing 

eralis 

i-.'B  iH  gs 

*-§o^ 

•i  oi  C  g 

3^3 

ft-   01   M 

rpus 
ppo 
iae 

arm 
t  pr 

5-t^«  n 

o  o^^  o 
O     w     2 

O 

'^       (D'^rii 


S     H 


nf 

O 

O 

"(i) 

fi 

4^ 

4J 

crt 

of 

(UJ3 

t3 

n 

o 

p. 

rt 

C 

ttP. 

rn 

w 

S 

rn 

rn 

o 

3 

S 

1^ 

rt 

(fl 

Fi 

^^►j 

ftcdls 


p-^ 


•o   a 


22 


^  0)        ^ 


2      tn       2 


ft„^S& 

.  Jg  fto  >> 

a.        2 


■ca 
al 

o 


m  o  o  o 

C  r%  u  "i 

O  iH       .  IH 

H  2 


•-■^      1-1^      (H^     O^ 

nj        g3        ni  "  gJ 

Wi  ir;  (-1  i-;  Ih  In  1-,  I- 
.!=(  +J.iH  -(J. in  +J.r^  4J. 
(U^   <u^   0)^   <D^ 


;  o  fi 

ftS 


i-e  ?^     -v^ 


.2  ft^  o 
t>  c 


jj  nj 


3  M 


m  ft 


£  bi  c3  bo 

tC  C       M  3"S 

be         T-i  +^  5 
j3_^    .  o  C  nj 

C  5  R  "  " 

ti  .  £  wi  .  S 

r!    P,+3    O+J    R 

"^  w  0)+^  R  O 
(«  w  ft  °  a'^ 


"d  jH         .3  R     .22 

<L>t2    _:  »-i   JD         4^ 

!3^  a       o  S       RO- 
SftO     ^.R^    .g,^ 

^Sa^^a 


•VboO 
bo  R  R 
R  J3  1- 
oi  bo  o 

o 


'5'-"  a 

o  iH  R 
B  O  <u  R 

213  bOM 
•R  lO  Dn 


S  <U        R 


'  "^"^  Rts 
2     <^^ 


fir^c 


O      d 


.2  >., 

o^ 

<J  fi 


M':3  R 
o  g.2 


fi;:? 

o  ft 


.fisRiest! 

ft  <u  «  tS 


•      THE  NERVOUS  SYSTE^il  547 

Marburg :  Atlas  des  menschlichen  Centralnervensystems,  Leipzig  and  Wein 
igio.  ' 

Meyer,  Adolf:  Critical  Review  of  the  Data  and  General  Methods  and 
Deductions  of  Modern  Neurology.  Journ.  of  Comp.  Neurol,  \o\  VIII  Nos  ^ 
and  4,  1898.  •  '         •  0 

Obersteiner:  Anleitung  beim  Studieren  des  Baues  der  nervosen  Central- 
organe,  Leipsic. 

Quain's  Elements  of  Anatomy,  Vol.  Ill,  Neurology,  Parts  i  and  2,  1908 
Ramon  y  Cajal:    Beitrag  zum  Studium  der  Medulla  Oblongata,  etc.,  Leipsic 
1896.— Les  nouvelles  idees  sur  la  structure  du  systeme  nerveux  chez  Thomme  et 
Chez  les  vertebres,  Paris,  i894.-Histologie  du  systeme  nerveux  de  1'  homme 
et  des  vertebres,  trad,  par  L.  Azoulay,  Tomes  I  and  II,  Paris.  1909. 
Studien  iiber  die  Hirnrinde  des  Menschen,  Leipsig,  1900. 

Spalteholz,  W.:  Handatlas  of  Human  Anatomy  (trans,  by  L.  F.  Barker) 
Vol.  Ill,  1903. 


CHAPTER  XIII 
THE  ORGANS  OF  SPECIAL  SENSE 

The  Organ  of  Vision 

The  eyeball  and  optic  nerve  constitute  the  organ  of  vision.  To 
be  described  in  connection  with  them  are  the  eyelid  and  the  lacrymal 
apparatus. 

The  Eyeball  or  Bulbus  Oculi. — This  is  almost  spherical,  although 
slightly  flattened  antero-posteriorly.  It  consists  of  a  wall  enclosing 
a' cavity  filled  with  fluid. 

The  wall  of  the  eyeball  consists  of  three  coats:  (a)  An  external 
fibrous  coat — the  sclera  and  cornea;  (b)  a  middle  vascular — the  cho- 
rioid;  and  (c)  an  internal  nervous — the  retina  (Fig.  358). 

The  Sclera  (Figs.  358  and  359).- — This  consists  of  dense  fibrous 
tissue  with  some  elastic  fibres.  The  fibres  run  both  meridionally 
and  equatorially,  the  tendons  of  the  straight  muscles  of  the  eyeball 
being  continuous  with  the  meridional  fibres,  those  of  the  oblique 
muscles  with  the  equatorial  fibres.  The  few  cells  of  the  sclera  lie 
in  distinct,  very  irregular  cell  spaces,  and  frequently  contain  pigment 
granules.  Pigmented  cells  in  considerable  numbers  are  regularly 
present  near  the  corneal  junction,  at  the  entrance  of  the  optic  nerve, 
and  on  the  inner  surface  of  the  sclera.  Where  the  optic  nerve  pierces 
the  sclera,  the  continuity  of  the  latter  is  broken  by  the  entering  nerve 
fibres,  forming  the  lamina  crihosa  (Fig.  367).  The  pigmented  layer 
of  the  sclera  next  the  chorioid  is  known  as  the  lamina  fusca,  and  is 
lined  internally  by  a  single  layer  of  flat  non-pigmented  endotheHum. 
Anteriorly  a  loose  connective  tissue  attaches  the  sclera  to  the  scleral 
conjunctiva. 

The  Cornea  (Figs.  360  and  363). — This  is  the  anterior  continua- 
tion of  the  sclera  so  modified  as  readily  to  allow  the  light  to  pass 
through  it.     It  is  about  i  mm.  thick  and  consists  of  five  layers,  which 
from  before  backward  are  as  follows  (Fig.  360) : 
(i)  Anterior  epithelium. 

(2)  Anterior  elastic  membrane  or  membrane  of  Bowman. 

(3)  Substantia  propria  cornese. 

548 


THE  ORGANS  OF  SPECIAL  SENSE  549 

(4)  Posterior  elastic  membrane  or  membrane  of  Descemet. 

(5)  Posterior  endothelium  or  endothelium  of  Descemet. 

(i)  The  anterior  epithelium  (Fig.  360,  i)  is  of  the  stratified  squa- 
mous type  and  consists  of  from  four  to  eight  layers  of  cells.  The 
deepest  cells  are  columnar  and  rest  upon  the  anterior  elastic  mem- 
brane.    The  middle  cells  are  polygonal  and  are  connected  by  short 


Fig  358. — Diagram  of  Ej^eball  showing  Coats.  (Mcrkel-Henle.)  a,  Sclera;  h, 
chorioid;  c,  relina;  d,  cornea;  e,  lens;/,  iris;  g,  conjunctiva;  h,  ciliary  body;  /,  sclero-cor- 
neal  junction  and  canal  of  Schlcmm;  j,  fovea  centralis;  k,  ojjtic  nerve. 

intercellular  bridges.     The  surface  cells  arc  flat.     Along  the  margin 
of  the  cornea  the  epithelium  is  continuous  with  that  of  the  conjunctiva 

(Fig-  363)- 

(2)  The  anterior  elastic  membrane  (Fig.  360,  2)  is  a  highly  de- 
veloped basement  membrane,  its  anterior  surface  being  pitted  to 
receive  the  bases  of  the  deepest  epithelial  cells.  It  is  apparently 
homogeneous,  and  while  called  an  elastic  membrane,  does  not  con- 
form chemically  to  either  fibrous  or  elastic  tissue.  By  means  of 
special  technic,  a  fibrillar  structure  has  been  demonstrated. 


550 


THE  ORGANS 


(3)  The  substantia  propria  (Fig.  360,  3)  constitutes  the  main 
bulk  of  the  cornea.  It  consists  of  connective  tissue  the  fibrils  of 
which  are  doubly  refracting  and  are  cemented  together  to  form 
bundles  and  lamellae.  In  the  human  cornea  the  lamellae  are  about 
sixty  in  number.  The  lamella  are  parallel  to  one  another  and  to  the 
surface  of  the  cornea,  but  the  fibres  of  adjacent  lamellae  cross  one 
another  at  an  angle  of  about  twelve  degrees.  The  lamellae  are  united 
by  cement  substance.  Fibres  running  obliquely  through  the 
lamellae  from  posterior  to  anterior  elastic  membranes  hold  the  lamellae 
firmly  together.     They  are  known  as  perforating  or  arcuate  fibres. 


Fig.  359. — Vertical  Section  through  Sclera,  Chorioid,  and  Pigment  Layer  of  Retina. 
(Merkel-Henle.)  A,  Sclera;  B,  chorioid;  C,  pigment  layer  of  retina;  d,  lamina  supra- 
chorioidea;  e,  HaUer's  layer  of  straight  vessels;/,  choriocapillaris;  g,  vitreous  membrane. 


Between  the  lamellae  are  irregular  flat  cell  spaces  which  commu- 
nicate with  one  another  and  with  the  lymph  spaces  at  the  margin  of 
the  cornea  by  means  of  canaliculi.  Seen  in  sections  vertical  to  the 
surface  of  the  cornea,  these  spaces  appear  fusiform.  In  the  spaces 
are  the  connective-tissue  cells  of  the  cornea  or  corneal  corpuscles. 
These  are  flat  cells  corresponding  in  shape  to  the  spaces  and  sending 
out  processes  into  the  canaliculi  (Figs.  361  and  362). 

(4)  The  posterior  elastic  membrane  or  membrane  oj  Descemet 
(Fig.  360,  4)  resembles  the  anterior,  but  is  much  thinner.  Like 
the  anterior,  it  does  not  give  the  chemical  reaction  of  elastic  tissue. 

(5)  The  posterior  endothelium  or  endothelium  oj  Descemet  (Fig. 
360,  5)  consists  of  a  single  layer  of  flat  hexagonal  cells,  the  nuclei 
of  which  frequently  project  slightly  above  the  surface. 

The  cornea  contains  no  blood-vessels. 

-The  Chorioid. — This  is  made  up  of  four  layers  which  from 
without  inward  are  as  follows  (Fig.  359) : 


THE  ORGANS  OF  SPECIAL  SENSE 


551 


of 


(i)  The  lamina  suprachorioidea. 

(2)  The  layer  of  straight  vessels — Haller's  layer. 

(3)  The  capillary  layer — choriocapillaris. 

(4)  The   vitreous    membrane — lamina    citrea — membrane 

Bruch. 
(i)  The  lamina  suprachorioidea  (Fig.  359,  d)  is  intimately  con- 
nected ^^dth  the  lamina  fusca  of  the  sclera  and  consists  of  loosely 
arranged  bundles  of  fibrous  and  elastic  tissue  among  which  are  scat- 
tered pigmented   and  non-pigmented 
connective- tissue    cells.        Numerous 
lymph  spaces  are  found  between  the 
bundles  of  connective  tissue  and  be- 
tween the  lamina  suprachorioidea  and 
lamina  fusca.     The  latter  are  known 
as    the    perichorioidal    lymph    spaces 
(Fig.  363). 

(2)  The  layer  of  straight  vessels  (Fig. 
359,  e)  consists  of  fibro-elastic  tissue 
containing  numerous  pigmented  and 
non-pigmented  cells,  supporting  the 
large  blood-vessels  of  the  layer.  The 
latter  can  be  seen  with  the  naked  eye, 
and,  as  they  are  straight  and  parallel, 
give  to  the  layer  a  striated  appearance. 
The  arteries  lie  to  the  inner  side.  The 
veins — vence  vorticosce — are  larger  than 
the  arteries  and  converge  toward  four 
points  one  in  each  quadrant  of  the 
eyeball. 

A  narrow  boundary  zone,  rich  in 
elastic  fibres  and  free  from  pigment, 

limits  this  layer  internally.  It  is  much  more  highly  developed  in 
some  of  the  lower  animals  than  in  man.  Formed  of  connective- 
ti.ssue  bundles  in  ruminants  and  horses,  it  is  known  as  the  tapetum 
fibrosum,  while  in  the  carnivora  its  structure — several  layers  of  flat 
cells — gives  it  the  name  of  the  tapetum^  cellulosum. 

(3)  The  choriocapillaris  (Fig.  359,/)  consists  of  connective  tissue 
supporting  a  dense  network  of  capillaries,  which  is  most  dense  in  the 
region  of  the  macula  lutca.  This  layer  is  usually  described  as  free  from 
pigment,  although  it  not  infrequently  contains  some  pigmented  cells. 


Fig.  360. — Vertical  Section  of 
Cornea.  (Merkel-Henle.)  i,  An- 
terior epithelium;  2,  anterior  elastic 
membrane;  3,  substantia  propria 
corneas;  4,  posterior  elastic  mem- 
brane; 5,  posterior  endothelium. 


552  THE  ORGANS 

(4)  The  vitreous  membrane  (Fig.  359,  g)  is  a  clear,  apparently 
structureless  membrane  about  two  microns  thick.  Its  outer  surface 
is  grooved  by  the  capillaries  of  the  choriocapillaris,  while  its  inner 
surface  is  pitted  by  the  retinal  epithelium. 


^         t       -^  ij  ■ 


■       &1% 


Fig.  361. — Section  of  Human  Cornea  cut  Tangential  to  Surface — X350  (technic  9,  p. 
97) — showing  corneal  cell  spaces  (lacunse)  and  anastomosing  canaliculi. 

The  Ciliary  Body. — This  is  the  anterior  extension  of  the  chorioid 
and  consists  of  the  ciUary  processes  and  the  ciliary  muscle  (Fig.  363). 
It  extends  from  the  ora  serrata  (a  wavy  edge  which  marks  the  anterior 


■>  '\ 


s 

s 

/         ' 

" 

-'»*  ^ 

/, 

Fig.  362. — Section  of  Human  Cornea  cut  Tangential  to  Surface — X3S0  (technic  8,  p. 
97) — showing  corneal  cells  and  their  anastomosing  processes. 

limit  of  the  nervous  elements  of  the  retina — see  Retina)  to  the  margin 
of  the  iris  (see  below). 

The  ciliary  processes  (Fig.  363),  from  seventy  to  eighty  in  number, 


THE  ORGANS  OF  SPECIAL  SENSE 


553 


are  meridionally-running  folds  of  the  chorioid  from  which  are  given 
off  numerous  irregular  secondary  folds.  The  processes  begin  low 
at  the  ora  serrata,  gradually  increase  in  height  to  about  i  mm.,  and 
end  abruptly  at  the  margin  of  the  iris.  The  ciliary  processes  consist 
of  connective  tissue  containing  many  pigmented  cells  and  supporting 
numerous  blood-vessels.  Invaginations  lined  with  clear  columnar 
epithelium  have  been  described  as  ciliary  glands.     The  ciliary  folds 


-Ins 

-Pars  indica  retiun 


Anterior  chamber- 


F^ 


Spaces  of  FonUna     |j|  ii  j ll\V\'¥^         ^"'•'^ ^ Cii 


Ciliary  process 

gainentura 
pectinatuin  iridis 

rciilar  fibres 
of  ciliary  muscle 


Conjunctiva' 


Radial  fibres  of 
ciliary  muscle 


Pars  ciliaris  retinae 


Perichorioidal  lymph  space. 


Orbiculus 
ciliaris 


Zonule  of  Zinn 


Fig.  363. — Vertical  Section  throu^l:  Human  Sclero-corneal  Junction.     (CunninKliam.) 


are  covered  by  the  vitreous  membrane,  and  internal  to  the  latter  is  a 
continuation  forward  of  non-nervous  elements  of  the  retina — pars 
ciliaris  retince  (Fig.  363).  This  consists  of  two  layers  of  columnar 
epithelial  cells,  the  outer  layer  being  pigmented,  the  inner  non- 
pigmentcd. 

The  ciliary  muscle  (Fig.  363)  is  a  band  of  smooth  muscle  which 
encircles  the  iris.  It  lies  in  the  odter  anterior  i)art  of  the  ciliary 
body,  and  on  cross  section  has  a  generally  triangular  shape.  It  is 
divisible  into  three  groups  of  muscle  cells:  (a)  An  inner  circular 
grouj)  near  the  base  of  the  iris—  circular  muscle  of  Miiller;   (h)   an 


554 


THE  ORGANS 


^ 


Sw 


outer  meridional  group  lying  next  to  the  sclera  and  known  as  the 
tenser  choricide^,  and  (c)  a  middle  radial  group.  The  meridional 
and  radial  groups  both  take  origin  in  the  posterior  elastic  lamina  of 
the  cornea,  the  former  passing  backward  along  the  margin  of 
the  sclera  to  its  insertion  in  the  ciliary  body  near  the  era  serrata,  the 
latter  radiating  fan-like  to  a  broad  insertion  in  the  cihary  body  and 
processes. 

The  ciliary  body  is  closely  attached  to  the  sclero-corneal  junction 
by  the  ligamentum  pectinatum   (Fig.   363),   a  continuation  of  the 

posterior  elastic  lamina  of  the 
cornea.  Within  the  ligament  are 
spaces  {spaces  of  Fontana)  lined 
with  endothelium.  These  are  ap- 
parently lymph  spaces,  and  com- 
municate with  each  other,  with 
similar  spaces  around  the  canal  of 
Schlemm,  and  with  the  anterior 
chamber.  The  canal  of  Schlemm 
(Fig.  363)  is  a  venous  canal  which 
encircles  the  cornea,  lying  in  the 
sclera  close  to  the  corneal  margin. 
Instead  of  a  single  canal  there  may 
be  several  canals. 

The  Iris  (Fig.  364).— This 
represents  a  further  continuation 
forward  of  the  chorioid.  Its  base 
is  attached  to  the  ciliary  body  and 
ligamentum  pectinatum.  From 
this  point  it  extends  forward  as  a 
diaphragm  in  front  of  the  lens,  its  centre  being  perforated  to  form  the 
pupillary  opening.  It  is  deeply  pigmented,  and  to  its  pigment  the 
color  of  the  eye  is  due.  Four  layers  may  be  distinguished,  which 
from  before  backward  are  as  follows: 
(i)  The  anterior  endothelium. 

(2)  The  stroma. 

(3)  The  vitreous  membrane. 

(4)  The  pigmented  epithelium. 

(i)  The  anterior  endothelium  is  a  single  layer  of  pigmented  cells 
continuous  with  the  posterior  endotheHum  of  the  cornea  (Fig. 
364,  a). 


J" 


Fig.  364. — Vertical  Section  through 
Iris.  (Merkel-Henle.)  a,  Anterior  en- 
dotheHum; h,  stroma  or  substantia  pro- 
pria; c,  vitreous  membrane;  d,  pigment 
layer;  v,  blood-vessel. 


THE  ORGANS  OF  SPECIAL  SENSE  555 

(2)  The  stroma  is  divisible  into  two  layers:  an  anterior  reticular 
layer,  containing  many  cells,  seme  of  which  are  pigmented,  and  a  vas- 
cular layer,  the  vessels  of  which  are  peculiar  in  that  their  walls  con- 
tain almost  no  muscle,  but  have  thick  connective-tissue  sheaths.  In 
the  posterior  part  of  the  stroma  are  bundles  of  smooth  muscle.  Those 
nearest  the  pupillary  margin  encircle  the  pupil,  forming  its  sphincter 
muscle,  while  external  are  scattered  radiating  bundles  forming  the 
dilator  muscle. 

(3)  The  vitreous  mcmhrane  is  continuous  with,  and  has  the  same 
structure  as  the  membrane  of  Bruch. 

(4)  The  pigmented  epithelium  (Fig.  364,  d)  consists  of  several 
layers  of  cells  and  is  continuous  with  the  pas  ciliaris  retinae.  Except 
in  albinos,  both  layers  are  pigmented. 

The  Retina. — The  retina  is  the  nervous  tunic  of  the  eye.  It 
lines  the  entire  eyeball,  ending  only  at  the  pupillary  margin  of  the 
iris.  Its  nervous  elements,  however,  extend  only  to  the  ora  serrata, 
which  marks  the  outer  limit  of  the  ciliary  body  (Fig.  363).  The 
nervous  part  of  the  retina  is  known  as  the  pars  optica  retincB,  the 
non-nervous  extension  over  the  ciliary  processes  as  the  pars  ciliaris 
rttincB,  its  further  continuation  over  the  iris  as  the  pars  iridica  retince. 
Modij&caticns  of  the  optic  portion  of  the  retina  are  found  in  the  region 
of  the  macula  lutea  and  of  the  optic  nerve  entrance. 

The  Pars  Optica  Retince. — This  is  the  only  part  of  the  retina 
directly  concerned  in  the  reception  of  impulses,  and  may  be  regarded 
as  the  extremely  complex  sensory  end-organ  of  the  optic  nerve.  It 
is  divisible  into  ten  layers,  which  from  without  inward  are  as  follows 
(Fig.  365): 

(i)  Layer  of  pigmented  epithelium. 

(2)  Layer  of  rods  and  cones. 

(3)  Outer  limiting  membrane.  [  I^ayer  of  neuro-epithelium. 

(4)  Outer  nuclear  layer. 

(5)  Outer  molecular  layer. 

(6)  Inner  nuclear  layer. 

(7)  Inner  molecular  layer. 

(8)  Layer  of  nerve  cells. 

(9)  Layer  of  nerve  fibres. 
(10)  Inner  limiting  membrane. 


Ganglionic  layer. 


The  layer  oj  pigmented  epithelium  (Fig.  365,  B,  i)  consists  of  a 
single  layer  of  regular  hexagonal  cells  (Fig.  25,  p.  76J.     The  nuclei 


556 


THE  ORGANS 


lie  in  the  outer  part  of  the  cell,  while  from  the  inner  side  thread-like 
projections  extend  down  between  the  rods  and  cones  of  the  layer  next 
internal.  The  pigment  has  the  form  of  rod-shaped  granules.  Its 
distribution  seems  to  depend  upon  the  amount  of  light  being  admitted 
to  the  retina.  When  little  or  no  light  is  being  admitted,  the  pigment 
is  found  in  the  body  of  the  cell,  the  processes  being  wholly  or  almost 


Fig.  365. — A,  Scheme  of  retina  as  shown  by  the  Golgi  method.  B,  Vertical  section 
of  retina  to  show  layers  as  demonstrated  by  the  haematoxylin-eosin  stain.  (Merkel- 
Henle.)  B. — i,  Layer  of  pigmented  epithelium;  2,  layer  of  rods  and  cones;  3,  outer 
limiting  layer;  4,  outer  nuclear  layer;  5,  outer  molecular  layer;  6,  inner  nuclear  layer;  7, 
inner  molecular  layer;  8,  layer  of  nerve  cells;  9,  layer  of  nerve  fibres;  10,  inner  limiting 
layer.  A. — i,  Pigment  layer;  2,  processes  of  pigmented  epithelial  cells  extending  down 
between  rods  and  cones;  3,  rods;  4,  rod-cell  nuclei  and  rod  fibres;  5,  cones;  6,  cone  fibres; 
7,  bipolar  cells  of  inner  nuclear  layer;  8,  ganglion  cells  of  nerve-cell  layer;  9,  larger  gang- 
lion cells  of  nerve-cell  layer;  10,  fibres  of  optic  nerve  forming  layer  of  nerve  fibres;  11 
and  12,  types  of  horizontal  cells;  13,  14,  15,  and  16,  types  of  cells  the  bodies  of  which  lie 
in  the  inner  nuclear  layer;  17,  efferent  optic-nerve  fibre  ending  around  cell  of  inner 
nuclear  layer;  18,  neuroglia  cells;  19,  MuUer's  fibre;  20,  rod-bipolar  cell  of  inner  nuclear 
layer. 


free  from  pigment;  when  the  retina  is  exposed  to  a  bright  light,  some 
of  the  pigment  granules  pass  down  into  the  processes  so  that  the  pig- 
ment becomes  more  evenly  distributed  throughout  the  cell. 

The  layer  oj  rods  and  cones  and  the  outer  nuclear  layer  (Fig.  365, 
J5,  2,4)  are  best  considered  as  subdivisions  of  a  single  layer,  the  neuro- 
epithelial layer.     This  consists  essentially  of  two  forms  of  neuro- 


THE  ORGANS  OF  SPECL\L  SENSE  557 

epithelial  elements,  rod  visual  cells  and  cone  visual  cells.  These,  with 
supporting  connective  tissue,  constitute  the  layer  of  rods  and  cones 
and  the  outer  nuclear  layer,  the  separation  into  sub-layers  being  due 
to  the  sharp  demarcation  between  the  nucleated  and  non-nucleated 
parts  of  the  cells,  and  the  separation  of  the  two  parts  by  the  per- 
forated outer  limiting  membrane. 

The  rod  visual  cell  (Fig.  365,  A,  4)  consists  of  rod,  rod-fibre,  and 
nucleus.  The  rod  (Fig.  365,  yl,  3)  is  a  cyhnder  from  30  to  40/^  in 
length  and  about  2/«  in  diameter.  It  is  divisible  into  an  outer  clear 
portion,  which  contains  the  so-called  "visual  purple"  and  an  inner 
granular  portion.  At  the  outer  end  of  the  latter  is  a  fibrillated  eUip- 
soidal  body,  much  more  distinct  in  some  of  the  lower  animals,  the 
ellipsoid  of  Krause.  At  its  inner  end  the  rod  tapers  down  to  a  line 
fibre,  the  rod  fibre,  which  passes  through  a  perforation  in  the  outer 
limiting  membrane  into  the  outer  nuclear  layer,  where  it  expands  and 
contains  the  nucleus  of  the  red  visual  cell.  These  nuclei  are  situated 
at  various  levels  in  the  fibre  and  constitute  the  most  conspicuous 
element  of  the  outer  nuclear  layer  (Fig.  365,  5,  4). 

The  cone  visual  cell  (Fig.  365,  A,  5,6)  consists  of  cone,  cone-fibre, 
and  nucleus.  The  cone  (Fig.  365,  yl,  5)  is  shorter  and  broader  than 
the  rod,  and  like  the  latter  is  divisible  into  two  parts.  The  outer  part 
is  short,  clear,  and  tapering,  the  inner  part  broad  and  granular,  and 
like  the  rod  contains  a  fibrillated  elhpsoid  body.  The  cone  fibre 
(Fig.  365,  y4,  6)  is  much  broader  than  the  rod  fibre,  passes  completely 
through  the  outer  nuclear  layer  and  ends  in  an  expansion  at  the  mar- 
gin of  the  outer  molecular  layer.  The  nucleus  of  the  cone  cell 
usually  lies   just  beneath  the  cuter  limiting  membrane. 

The  remaining  layers  of  the  retina  must  be  considered  in  relation 
on  the  one  hand  to  the  neuro-epitheUum,  on  the  other  to  the  optic 
nerve.  The  inner  nuclear  layer  (Fig.  365,  B,  6)  and  the  layer  of  nerve 
cells  (Fig.  365,  B,  8)  are  composed  largely  of  nerve-cell  bodies,  while 
the  two  molecular  layers  (Fig.  365,  B,  5,  7)  are  formed  mainly  of  the 
ramifications  of  the  processes  of  these  cells.  In  the  inner  nuclear 
layer  are  two  kinds  of  nerve  elements,  rod  bipolar  cells  and  cone  bipolar 
cells.  The  bodies  of  these  cells  with  their  large  nuclei  form  the  bulk 
of  this  layer.  From  the  rod  bipolars  (Fig.  365,  yl,  20)  processes 
(dendrites)  pass  outward  to  ramify  in  the  outer  molecular  layer 
around  the  terminations  of  the  rod  fibres.  From  the  cone  bipolars 
("Fig.  3O5,  A,  7)  similar  processes  (dendrites)  extend  into  the  outer 
molecular  layer  where  they  ramify  around  the  terminations  of  the 


558  THE  ORGANS 

cone  cells.  Two  other  forms  of  nerve  cells  occur  in  the  inner  nu- 
clear layer.  One  is  known  as  the  horizontal  cell  (Fig.  365,  A,  12). 
Its  processes  ramify  almost  wholly  in  the  outer  molecular  layer. 
The  other  lies  along  the  inner  margin  of  the  inner  nuclear  layer  and 
sends  its  dendrites  into  the  inner  molecular  layer  (Fig.  365,  A,  13, 
14,  15,  and  16).  Many  of  these  latter  cells  appear  to  have  no  axone 
and  are  consequently  known  as  amacrine  cells. 

The  outer  molecular  layer  is  thus  seen  to  be  formed  mainly  of 
terminations  of  the  rod  and  cone  visual  cells,  of  the  dendrites  of  the 
rod  and  cone  bipolars,  and  of  the  processes  of  the  horizontal  cells. 

From  the  cone  bipolar  a  process  {axone)  extends  inward  to  ramify 
in  the  inner  molecular  layer,  while  from  the  rod  bipolar  a  process 
(axone)  passes  inward  through  the  inner  molecular  layer  to  terminate 
around  the  cells  of  the  nerve- cell  layer. 

The  layer  of  nerve  cells  (Fig.  365,  B,  8)  consists  for  the  most  part 
of  large  ganglion  cells  whose  dendrites  ramify  in  the  inner  molecular 
layer,  and  whose  axones  pass  into  the  layer  of  nerve  fibres  and 
thence  into  the  optic  nerve.  Some  small  ganglion  cells  are  also  found 
in  this  layer,  especially  in  the  region  of  the  macula  lutea  (see  page  559) . 

The  inner  molecular  layer  is  thus  seen  to  be  composed  mainly 
of  the  processes  {axones)  of  the  rod  and  cone  bipolars  and  of  the  den- 
drites of  the  ganglion  cells  of  the  nerve-cell  layer. 

The  layer  oj  nerve  fibres  (Fig.  365,  5,  9)  consists  mainly  of  the  ax- 
ones of  the  just-described  ganglion  cells,  although  a  few  centrifugal 
axones  of  brain  cells  (Fig.  365,  A,  17)  are  probably  intermingled. 

The  outer  and  inner  limiting  layers  or  membranes  (Fig.  365,  B,  3,10) 
are  parts  of  the  sustentacular  apparatus  of  the  retina,  being  connected 
with  the  cells  or  fibres  of  Muller  (Fig.  365,  ^,19  and  Fig.  366).  The 
latter  form  the  most  conspicuous  elements  of  the  supportive  tissue  of 
the  retina.  They  are  like  the  nerve  elements  proper,  of  ectodermic 
origin  and  are  elongated  cells  which  extend  through  all  the  retinal 
layers,  excepting  the  layer  of  rods  and  cones  and  the  pigment  layer. 
The  inner  ends  of  the  cells,  which  are  conical  and  fibrillated,  unite  to 
form  the  inner  limiting  membrane  (Fig.  366,  10).  Through  the  inner 
molecular  layer  the  cell  takes  the  form  of  a  narrow  stalk  with  nu- 
merous fringe-like  side  fibrils  (Fig.  366,  7).  This  widens  in  the  inner 
nuclear  layer,  where  cup-Hke  depressions  in  the  sides  of  the  Muller 's 
cell  are  caused  by  the  pressure  of  the  surrounding  nerve  cells  (Fig. 
366,  b).  This  wide  portion  of  the  cell  in  the  inner  nuclear  layer  con- 
tains the  nucleus  (Fig.  366,  a).     In  the  outer  jnolecular  layer  the 


THE  ORGANS  OF  SPECI.\L  SENSE 


559 


cell  again  becomes  narrow  (Fig.  366,  5)  and  in  the  outer  nuclear  layer 
broadens  out  into  a  sponge-like  reticulum  (Fig.  366,  4),  which  sup- 
ports the  rod  and  cone  bipolars.  At  the  inner  margin  of  the  layer  of 
rods  and  cones  the  protoplasm  of  the  Mliller's  cells  spreads  out  and 
unites  to  form  the  so-called  outer  hmiting  membrane  (Fig.  366,  3), 
from  which  delicate  fibrils  (fibre  baskets)  pass  outward  between  the 

rods  and  cones.  In  addition  to  the  Mlil- 
ler's cells,  which  are  neuroglia  elements, 
spider  cells  also  occur  in  the  retina  (Fig. 
365,^,18). 

The  retina  of  the  macula  lutea  presents 
certain  peculiarities.  Its  name  is  derived 
from  the  yellow  pigment  which  is  dis- 
tributed diffusely  through  the  inner  layers, 
extending  as  far  out  as  the  outer  mole- 
cular layer.  The  ganglion-cell  layer  and 
the  inner  nuclear  layer  are  thicker  than  in 
other  parts  of  the  retina.  In  the  layer  of 
rods  and  cones  there  is  a  gradual  re- 
daction in  the  number  of  rods,  while 
the  number  of  cones  is  correspondingly 
increased. 

In  the  centre  of  the  macula  is  a  depres- 
sion, the  jovea  centralis.  As  the  retina 
approaches  this  area  it  becomes  greatly 
thinned,  little  remaining  but  the  layer  of 
cone  cells  and  the  somewhat  thickened 
layer  of  pigmented  epithelium. 

At  the  ora  serrata  the  nervous  elements 
of  the  retina  cease.  The  non-nervous  ret- 
inal extension  over  the  ciliary  body  {pars 
ciliaris  relince)  and  over  the  iris  {pars 
iridica  relince)  have  been  described  in  con- 
nection with  the  ciHary  body  and  iris. 
The  Optic  Nerve. — The  optic  nerve  (Fig.  367,  d)  is  enclosed  by 
two  connective-tissue  sheaths,  both  of  which  are  extensions  of  the 
brain  membranes.  The  outer  or  dural  sheath,  (Fig.  367,  a)  is  continu- 
ous with  the  dura  mater  of  the  brain  posteriorly,  while  anteriorly  it 
blends  with  the  sclera.  The  inner  or  pial  sheath,  (Fig.  367,  b)  is  an  ex- 
tension of  the  pia  mater  and  is  separated  from  the  outer  sheath  by 


Fig.  366.— Two  MuUer's 
Fibres  from  Retina  of  Ox 
showing  Relation  to  Layers  of 
Retina.  (Ramon  y  Caj'al.) 
3,  Outer  limiting  layer;  4, 
outer  nuclear  layer;  5,  outer 
molecular  layer;  6,  inner  nu- 
clear layer;  7,  inner  molecular 
layer;  8,  layer  of  nerve  cells; 
9,  layer  of  nerve  fibres;  10,  in- 
ner limiting  layer;  a,  nucleus; 
b,  cup-like  depression  caused 
by  pressure  from  surrounding 
cells. 


560 


THE  ORGANS 


the  subdural  space  (Fig.  367,  c).  The  pial  sheath  is  divisible  into 
two  sub-layers:  an  outer  fibrous  layer  (the  so-called  arachnoid),  and 
an  inner  vascular  layer.  These  two  layers  are  separated  by  a  narrow 
space,  the  subarachnoid  space.  The  optic  nerve  fibres,  in  passing 
through   the  sclera   and    chorioid,   separate    the    connective-tissue 

bundles  so  that  they  form 
a  lattice-work,  the  already 
mentioned  lamina  crihrosa 
(Fig.  367,  h).  The  optic 
nerve  fibres  are  medullated, 
but  have  no  neurilemma. 
As  they  pass  through  the 
lamina  cribrosa  the  medul- 
lary sheaths  are  lost,  the 
fibres  reaching  the  retina  as 
naked  axones. 

Relations  of  Optic  Nerve 
TO  Retina  and  Brain 

The  rod  and  cone  visual 
cells  are  the  neuro-epithelial 
beginnings  of  the  visual 
tract  (Fig.  365,  A,  3,  4,  5, 
and  6).  By  their  expanded 
bases  in  the  outer  molecular 
layer,  the  rod  and  cone  cells 

Fig.  367.-Section  through  Entrance  of  Optic     communicate  with  the  neu- 
Nerve  into  Eyeball.    (Merkel-Henle.)     a,  Dural     (-^--iii^i^^^" 

sheath;  b,  pial  sheath,  inner  and  outer  layers;  c,  ^onc  System  No.'  I.  of  the 
space  between  inner  and  outer  layers  of  pia  mater;  ^-^„^f       ^W^c  rr,mr>ri<;pQ 

(/,  optic  nerve;  e,  central  artery  of  retina;  a',  OptlC  tract.  i  lllS  COmpriSeS 
sclera;  /,  chorioid;  ,  retina;  h,  lamina  cribrosa.       ^^-^     ^^^    neurones,     (&)     COne 

neurones,  (c)  horizontal  neurones. 

Neurone  System  No.  L— (a)  Rod  neurones.  The  cell  bodies 
of  these  neurones  (Fig.  365,  A,  20)  He  in  the  inner  nuclear  layer. 
Their  dendrites  enter  the  outer  molecular  layer  where  they  form  net- 
works around  the  expanded  bases  of  the  rod  cells.  Their  axones  pass 
through  the  inner  molecular  layer  and  end  in  arborizations  around  the 
bodies  and  dendrites  of  cells  of  the  nerve-cell  layer  (neurone  system 
No.  II.).  {h)  Cone  neurones  (Fig.  365,  ^,7).  These  have  their  cell 
bodies  in  the  inner  nuclear  layer.  Their  dendrites  pass  to  the  outer 
molecular  layer  where  they  form  networks  around  the  expanded  bases 


THE  ORGANS  OF  SPECIAL  SENSE 


561 


of  the  cone  cells.  Their  axones  pass  only  into  the  inner  molecular 
layer  where  they  end  in  arborizations  around  the  dendrites  of  neu- 
rones whose  cell  bodies  are  in  the  layer  of  nerve  cells  (neurone  system 
Xo.  II.).  (c)  Horizontal  neurones  (Fig.  365,  A,  11  and  12).  These 
serve  as  association  neurones  between  the  visual  cells  and  may  be 
divided  into  rod  association  neu- 
rones and  cone  association  neu- 
rones. The  cone  association 
neurones  are  the  smaller  and 
more  superficial,  and  both  den- 
drites and  axones  end  in  the 
outer  molecular  layer  around  the 
terminal  expansions  of  the  cone 
visual  cells  (Fig.  365,  A,  11). 
The  rod  association  neurones  are 
larger,  more  deeply  seated,  and 
behave  in  a  similar  manner  to- 
ward the  rod  visual  cells  (Fig. 
365,  A,  12).  Some  of  these  cells 
send  processes  to  the  inner  mole- 
cular layer. 

Neurone  System  No.  II. — 
This  has  been  already  partly  de- 
scribed in  connection  with  the 
axone  terminations  of  neurone 
system  No.  I.  The  cell  bodies 
neurone    system 

8,   9)    are   in  the 
cells  and  are,  as 

associated     either 


Fig.  368. — Diagram  showing  Main 
Relations  of  Optic  Tract.  (Testut.) 
R,  Retina;  No,  optic  nerve;  CM,  optic 
decussation  or  chiasma;  Tro,  optic  tract; 
Tho,  thalamus;  Cgl,  lateral  geniculate 
body;  Qa,  anterior  corpus  quadrigemi- 
num;  Rd,  fibre  of  optic  tract  passing 
directly  to  cortex;  Sm,  third  neurone  sys- 
tem of  optic  tract  (excepting  Rd)  connect- 
ing thalamus,  lateral  geniculate  body, 
and  anterior  corpus  quadrigemnium  with 
the  cortex,  Co. 


of    the    second 

(Fig.   365,   A,   , 

layer  of  nerve 

above    noted, 

directly    or    by    means    of    their 

dendrites  with  the  axones  of  the 

first     neurone     system.       Their 

axones  pass  into  the  layer  of  nerve  fibres  and  ultimately  become 

fibres  of  the  optic  nerve  (Fig.  365,  A,  10). 

The  optic  nerves  (Fig.  368,  No)  unite  at  the  base  of  the  brain  to 
form  the  optic  decussation  or  chiasma  (Fig.  368,  CM).  Here  the 
axones  from  the  mesial  j)art  of  the  retina  cross  to  the  optic  tract  of 
the  opposite  side,  while  those  from  the  lateral  part  of  the  retina  remain 
in  the  optic  tract  of  the  same  side.  The  axones  of  the  optic  tract 
36 


562 


THE  ORGANS 


Uoffer  ■ 


Fig.  3^ 


THE  ORGANS  OF  SPECL\L  SENSE  563 


EXPLANATION  OF  FIG.  369. 

Fig.  369. — Diagram  of  the  Optic  Nerve  (II)  and  some  of  its  Principal  Connections. 
A,  Level  of  nerves  II  and  III;  B,  level  of  nerve  IV;  C,  level  of  nerves  VI  and  VII;  D, 
spinal  cord.  The  rods  and  cones  (sensory  cells)  and  the  bipolar  cells  (  =  Neurone  No.  i) 
of  the  retina  are  not  indicated. 

Neurone  No.  2. —  2  a,  Axones  of  ganglion  cells  in  temporal  part  of  retina  pass  to  pul- 
vinar  of  thalamus  of  same  side;  2  b,  axones  of  ganglion  cells  in  retina  pass  to  anterior  corpus 
quadrigeminum  of  same  side;  2  c,  axones  of  ganglion  cells  in  retina  pass  to  external 
geniculate  bodj^  (Corp.  gen.  ext.)  of  same  side;  2  e,  axones  of  ganglion  cells  in  nasal  side  of 
retina  cross  in  optic  chiasma  and  pass  to  external  geniculate  body  of  opposite  side;  2/, 
axones  of  ganglion  cells  in  nasal  side  of  retina  cross  in  optic  chiasma  and  pass  to  anterior 
corpus  quadrigeminum  of  opposite  side;  2  g,  axones  of  ganglion  cells  in  nasal  side  of  retina 
cross  in  optic  chiasma  and  pass  to  pulvinar  of  thalamus  of  opposite  side. 

Neurone  No.  3. — 3  a,  Axones  of  cells  in  pulvinar  to  cortex  of  occipital  lobe  of  cere- 
brum (this  connection  is  disputed);  3  b,  axones  of  cells  in  external  geniculate  body  to 
cortex  of  occipital  lobe  of  cerebrum;  3  a  and  3  b  constitute  the  primary  optic  radiation; 
3  c,  2,  d  and  3  c,  axones  of  cells  in  middle  layer  of  tectum  (roof)  of  anterior  corpus  quad- 
rigeminum decussate  ventral  to  posterior  longitudinal  fasciculus  (dorsal  tegmental 
decussation  or  decussation  of  IMeynert)  and  form  the  tractus  lecto-bulbarlis  et  spinalis 
(Tr.  tecto-bulb.  et  spin.)  to  bulb  (medulla)  and  anterior  column  of  cord,  innervating 
by  collaterals  and  terminals,  directly  or  indirectly,  chief!)-  the  nuclei  of  III,  I\',  \T,  and 
VII  cranial  nerves  and  motor  nuclei  of  spinal  nerves.  3  /  and  3  g  (possibly  another 
neurone  intercalated  between  these  and  optic  terminals),  axones  of  cells  in  nucleus  of 
posterior  longitudinal  fasciculus  (Nu.  fasc.  long,  post.)  (Nucleus  of  Darkschewitsch) 
form  part  of  posterior  longitudinal  fasciculus  and  descend  on  same  side  to  anterior 
column  of  cord  next  to  anterior  median  fissure,  innervating  nuclei  of  III,  IV,  and  VI 
cranial  ner\'es  and  motor  nuclei  of  spinal  nerves. 

Neuronic  No.  4. — -Axones  of  cells  in  above-mentioned  motor  nuclei.  Axones  from 
cells  in  median  nucleus  of  III  nerve  (Nu.  med.  Ill  N.  ),  and  possibly  in  Edinger-West- 
phal  nucleus,  probably  innervate  the  intrinsic  muscles  of  eyeball  (ciliary  and  pupillary 
reflex  path). 

It  is  evident  from  the  diagram  that  the  cerebral  pathway  of  the  optic  nerve  is  via  the 
external  geniculate  body  (and  pulvinar  of  thalamus),  and  the  reflex  pathway  in  via  the 
anterior  colliculus  (anterior  corpus  quadrigeminum). 


564 


THE  ORGANS 


(Fig.  368,  Tro)  terminate  in  the  thalamus,  in  the  lateral  geniculate 
body,  and  in  the  anterior  corpus  quadrigeminum  (Fig.  368). 

Neurone  System  No.  III.^ — The  neurones  of  this  system  have 
their  cell  bodies  in  the  thalamus,  lateral  geniculate  body,  and  anterior 
corpus  quadrigeminum  (Fig.  368).  The  axones  of  the  two  former 
terminate  in  the  cortical  visual  centers  in  the  occipital  lobe  (Fig.  368, 
Co).  The  axones  of  the  latter  form  descending  reflex  paths  (see 
Anterior  Corpora  Quadrigemina,  p.  522). 

Neurone  system  No.  I  is  the  analog  of  the  primary  afferent  neu- 
j    c       a  rones   (the    cerebro-spinal    ganglion 

cells).  Neurone  system  No.  II  is 
the  analog  of  the  secondary  afferent 
neurone  system  which  receives  the 
afferent  root  fibres  and  originates 
the    secondary    decussating     tracts 


Fig-  370.  Fig.  371. 

Fig.  370. — From  Longitudinal  Section  through  Margin  of  Crystalline  Lens,  showing 
longitudinal  sections  of  lens  fibres  and  transition  from  epithelium  of  capsule  to  lens 
fibres.     (Merkel-Henle.)     a,  Lens  fibres;  h,  capsule;  c,  epithelium. 

Fig.  371. — From  Cross  Section  of  Crystalline  Lens,  showing  transverse  sections  of 
lens  fibres  and  surface  epithehum.     (Merkel-Henle.)     a,  Lens  fibres;  h,  epithelium. 

to  the  thalamus,  such  as  the  medial  and  lateral  fillets.  Neu- 
rone system  No.  Ill  is  the  tertiary  afferent  neurone  system  or 
thalamo-cortical  system.  It  will  thus  be  seen  that  the  optic  chiasma 
is  the  analog  of  the  decussations  of  the  medial  and  lateral  fillets. 
(See  also  pp.  475,  476  A.) 

The  Lens. — The  lens  is  composed  of  lens  fibres  which  are  laid 
down  in  layers  (Fig.  370,  a).  The  lens  fibre  is  a  long  hexagonal,  flat- 
tened prism  with  serrated  edges.     Most  of  the  lens  fibres  are  nucle- 


THE  ORGANS  OF  SPECI.AJL  SENSE  565 

ated,  the  nucleus  lying  at  about  the  centre  of  the  fibre  near  the  axis 
of  the  lens.  The  most  central  of  the  lens  fibres  are  usually  non- 
nucleated.  The  fibres  extend  meridionally  from  before  backward 
through  the  entire  thickness  of  the  lens.  They  are  united  by  a  small 
amount  of  cement  substance.  The  lens  is  surrounded  by  the  lens 
capsule  (Fig.  370,  b),  a  clear  homogeneous  membrane  which  is  about 
i2«  thick  over  the  anterior  surface  of  the  lens,  about  half  as  thick 
over  the  posterior  surface.  Between  the  capsule  and  the  anterior  and 
lateral  surfaces  of  the  lens  is  a  single  layer  of  cuboidal  epithelial  cells 
(Fig.  370,  c),  the  lens  epithelium.  Attached  to  the  capsule  of  the  lens 
anteriorly  and  posteriorly  are  membrane-like  structures  which  con- 
stitute the  suspensory  ligament  of  the  lens.  These  pass  outward  and 
unite  to  form  a  delicate  membrane,  the  zonula  ciliaris  or  zonule  of 
Zinn  (Fig.  363).  This  bridges  over  the  inequalities  of  the  ciliary 
processes  and,  continuing  as  the  hyaloid  membrane,  forms  a  lining  for 
the  vitreous  cavity  of  the  eye.  The  triangular  space  between  the 
two  layers  of  the  suspensory  ligament  and  the  lens  is  known  as  the 
canal  of  Petit. 

The  vitreous  body  is  a  semifluid  substance  containing  fibres  which 
run  in  all  directions  and  a  small  number  of  connective-tissue  cells  and 
leucocytes.  Traversing  the  vitreous  in  an  antero-posterior  direction 
is  the  so-called  hyaloid  or  CloqueVs  canal,  the  remains  of  the  embry- 
onic hyaloid  artery  (page  570). 

Blood-vessels. — The  blood-vessels  of  the  eyeball  are  divisible 
into  two  groups,  one  group  being  branches  of  the  central  artery  of  the 
retina,  the  other  being  branches  of  the  ciliary  artery. 

The  central  artery  of  the  retina  enters  the  eyeball  through  the 
centre  of  the  optic  nerve.  Within  the  eyeball  it  divides  into  two 
branches,  a  superior  and  an  inferior.  These  pass  anteriorly  in  the 
nerve-fibre  layer,  giving  off  branches,  which  in  turn  give  rise  to  capil- 
laries which  supply  the  retina,  passing  outward  as  far  as  the  neuro- 
epithelial layer  and  anteriorly  as  far  as  the  ora  serrata.  The  smaller 
branches  of  the  retinal  arteries  do  not  anastomose.  In  the  embryo 
a  third  vessel  exists,  the  hyaloid  artery.  This  is  a  branch  of  the  cen- 
tral retinal  artery  and  traverses  the  vitreous  to  the  posterior  surface 
of  the  lens,  supplying  these  structures.  The  hyaloid  canal,  or  canal 
of  Cloquet,  of  the  adult  vitreous,  represents  the  remains  of  the  degen- 
erate hyaloid  artery  (page  570).  The  veins  of  the  retina  accompany 
the  arteries. 

The  cih'ary  arteries  are  divisible  into  long  ciUary  arteries,  short 


566  •  THE  ORGANS 

ciliary  arteries,  and  anterior  ciliary  arteries.  The  long  ciliary  arte- 
ries are  two  in  number  and  pass  one  on  each  side  between  the  cho- 
rioid  and  sclera  to  the  ciliary  body,  where  each  divides  into  two 
branches,  which  diverge  and  run  along  the  ciliary  margin  of  the  iris. 
Here  the  anastomosis  of  the  two  long  ciHary  arteries  forms  the  greater 
arterial  circle  of  the  iris.  This  gives  rise  to  small  branches  which 
pass  inward  supplying  the  surrounding  tissues  and  unite  near  the 
margin  of  the  pupil  to  form  the  lesser  arterial  circle  of  the  iris.  The 
branches  of  the  short  ciliary  arteries  pierce  the  sclera  near  the  optic 
nerve  entrance,  supply  the  posterior  part  of  the  sclera,  and  terminate 
in  the  chorio-capillaris  of  the  chorioid.  The  anterior  ciliary  arteries 
enter  the  sclera  near  the  corneal  margin  and  communicate  with  the 
chorio-capillaris  and  with  the  greater  arterial  circle  of  the  iris.  The 
anterior  cihary  arteries  also  supply  the  ciliary  and  recti  muscles  and 
partly  supply  the  sclera  and  conjunctiva.  Small  veins  accompany 
the  ciliary  arteries;  the  larger  veins  of  this  area  are  peculiar,  however, 
in  that  they  do  not  accompany  the  arteries,  but  as  venae  vorticosae 
converge  toward  four  centres,  one  in  each  quadrant  of  the  eyeball. 
At  the  sclero- corneal  junction  is  a  venous  channel,  the  canal  of 
Schlemm,  which  completely  encircles  the  cornea  (Fig.  363). 

Lymphatics. — The  eyeball  has  no  distinct  lymph-vessel  system. 
The  lymph,  however,  follows  certain  definite  directions  which  have 
been  designated  by  Schwalbe  "lymph  paths."  He  divides  them 
into  anterior  lymph  paths  and  posterior  lymph  paths.  The  anterior 
lymph  paths  comprise  {a)  the  anterior  chamber  which  communi- 
cates by  means  of  a  narrow  cleft  between  iris  and  lens  with  the 
posterior  chamber;  {h)  the  posterior  chamber;  (c)  the  lymph  canal- 
icuH  of  the  sclera  and  cornea  and  the  canal  of  Petit.  The  posterior 
lymph  paths  include  {a)  the  hyaloid  canal  (see  above) ;  (&)  the  sub- 
dural and  intra-pial  spaces,  including  the  capsule  of  Tenon;  {c)  the 
perichorioidal  space,  and  {d)  the  perivascular  and  pericellular  lymph 
spaces  of  the  retina. 

Nerves. — The  nerves  which  supply  the  eyeball  pass  through  the 
sclera  with  the  optic  nerve  and  around  the  eyeball  in  the  supra- 
chorioid  layer.     From  these  nerves,  branches  are  given  off  as  follows: 

(i)  To  the  chorioid,  where  they  are  intermingled  with  ganglion 
cells. 

(2)  To  the  ciHary  body,  where  they  are  mingled  with  ganglion 
cells  to  form  the  ciliary  plexus.  The  latter  gives  off  branches  to  the 
ciliary  body  itself,  to  the  iris,  and  to  the  cornea.     Those  to  the 


THE  ORGANS  OF  SPECIAL  SENSE  567 

cornea  first  form  a  plexus  in  the  sclera — the  plexus  annularis — which 
encircles  the  cornea.  From  this,  branches  pierce  the  substantia 
propria  of  the  cornea,  where  they  form  four  corneal  plexuses,  one  in 
the  posterior  part  of  the  substantia  propria,  a  second  just  beneath 
the  anterior  elastic  membrane,  a  third  sub-epitheUal,  and  a  fourth 
intra-epithelial.  The  fibres  of  the  last  named  are  extremely  delicate 
and  terminate  freely  between  the  epithelial  cells.  Krause  describes 
end-bulbs  as  occurring  in  the  substantia  propria  near  the  margin 
of  the  sclera,  while  according  to  Dogiel  some  of  the  fibres  are  con- 
nected with  end-plates. 

The  Lacrymal  Apparatus 

The  lacrymal  apparatus  of  each  eye  consists  of  the  gland,  its 
excretory  ducts,  the  lacrymal  canal,  the  lacrymal  sac,  and  the  nasal 
duct. 

The  lacrymal  gland  is  a  compound  tubular  gland  consisting  of 
two  main  lobes.  Its  structure  corresponds  in  general  to  that  of  a 
serous  gland.  The  excretory  ducts  are  lined  with  a  two-layered  col- 
umnar epithelium  which  becomes  simple  columnar  in  the  smaller 
ducts.  The  alveoH  are  fined  with  irregularly  cuboidal  serous  cells, 
which  rest  upon  a  basement  membrane  beneath  which  is  a  richly 
elastic  interstitial  tissue. 

The  lacrymal  canals  have  a  stratified  squamous  epithelial  lining. 
This  rests  upon  a  basement  membrane  beneath  which  is  the  stroma 
containing  many  elastic  fibres.  External  to  the  connective  tissue  are 
some  longitudinal  muscle  fibres. 

The  lacrymal  sac  is  fined  with  a  two-layered  stratified  or  pseudo- 
stratified  columnar  epithefium  resting  upon  a  basement  membrane. 
The  stroma  contains  much  diffuse  lymphatic  tissue. 

The  nasal  duct  has  walls  similar  in  structure  to  those  of  the  lacry- 
mal sac.  In  the  case  of  both  sac  and  duct  the  walls  abut  against 
periosteum,  a  dense  vascular  plexus  being  interposed. 

The  blood-vessels,  lymphatics,  and  nerves  of  the  lacrymal  gland 
have  a  distribution  similar  to  those  of  other  serous  glands. 

The  EYELm 

The  eyelid  consists  of  an  outer  skin  layer,  an  inner  conjunctival 
layer,  and  a  middle  connective-tissue  layer. 

The  epidermis  is  thin  and  the  papillx'  of  the  derma  are  low.  Small 
sebaceous  glands,  sweat  glands,  and  fine  hairs  are  present. 


568 


THE  ORGANS 


The  conjunctiva  (Fig.  372,  d)  is  a  mucous  membrane  consisting 
of  a  lining  epithelium  and  a  stroma.  The  epithelium  is  stratified 
columnar  consisting  of  two  or  three  layers  of  cells.     Among  these 

cells  are  cells  resembling  gob- 
let cells.  Although  not  always 
up6n  the  surface,  they  are 
believed  to  be  mucous  cells, 
probably  analogous  to  the 
so-called  Leydig's  cells  found 
in  the  larvae  of  amphibians 
and  fishes.  Diffuse  lymphoid 
tissue  is  regularly  present  in 
the  stroma,  while  lymph 
nodules  are  of  rare  occur- 
rence. Small  glands,  similar 
to  the  lacrymal  glands  in 
structure,  are  usually  present 
(Fig.  372,  k). 

At  the  margin  of  the  eye- 
lid where  skin  joins  mucous 
membrane  are  several  rows  of 
large  hairs,  the  eyelashes  (Fig. 
372,  h).  Connected  with 
their  follicles  are  the  usual 
sebaceous  glands  (Fig.  372,  g) 
and  the  glands  of  Mall,  the 
latter  probably  representing 
modified  sweat  glands. 

The  middle  layer  contains 
the  tarsus  (Fig.  372,  e)  and 
the  muscular  structure  of  the 
eyehd  (Fig.  372,  b).  The 
tarsus  is  a  plate  of  dense 
fibrous  tissue  which  lies  just 
beneath  the  conjunctiva  and 
extends  about  two-thirds  the 
height  of  the  Hd.  It  contains  the  tarsal  or  Meibomian  glands  (Fig. 
372,  e).  These  are  from  thirty  to  forty  in  number,  each  consisting 
of  a  long  duct  which  opens  externally  on  the  margin  of  the  lid  behind 
the  lashes  (Fig.  372,/),  and  internally  into  a  number  of  branched 


Fig.  372. — Vertical  Section  through  Upper 
Eyelid.  (Waldeyer.)  a,  Skin;  b,  orbicularis 
muscle;  b',  ciliary  bundle  of  muscle;  c,  in- 
voluntary muscle  of  eyelid;  d,  conjunctiva;  e, 
tarsus  _  contaning  Meibomian  glands;  /,  duct 
of  Meibomian  gland;  g,  sebaceous  gland  with 
duct  lying  near  eyelashes;  h,  eyelashes;  i, 
small  hairs  in  outer  skin;j,  sweat  glands;  k, 
posterior  tarsal  glands. 


THE  ORGANS  OF  SPECIAL  SENSE 


569 


tubules.  The  duct  is  lined  with  stratified  squamous  epithelium. 
The  tubules  resemble  those  of  the  sebaceous  glands.  Between  the 
tarsus  and  the  skin  are  the  muscular  structures  of  the  eyelid  in 
which  both  smooth  and  striated  muscle  are  found. 

Blood-vessels. — ^Two  main  arteries  pass  to  the  eyelid,  one  at 
each  angle,  and  unite  to  form  an  arch,  the  tarsal  arch,  along  the 
margin  of  the  Hd.  A  second  arch,  the  external  tarsal  arch,  is  formed 
along  the  upper  margin  of  the  tarsus.  From  these  arches  are  given 
ofif  capillary  networks  which  supply  the  structures  of  the  lid. 

Lymphatics. — These  form  two  anastomosing  plexuses,  one  ante- 
rior, the  other  posterior  to  the  tarsus. 

Nerves. — The  nerves  form  plexuses  in  the  substance  of  the  lid. 
From  these,  terminal  fibrils  pass  to  the  various  structures  of  the  lid. 
Many  of  the  fibres  end  freely  in  fine  networks  around  the  tarsal 
glands,  upon  the  blood-vessels,  and  in  the  epithelium  of  the  conjunc- 
tiva. Other  fibres  terminate  in  end-bulbs  which  are  especially  nu- 
merous at  the  margin  of  the  Hd. 

Development  of  the  Eye 

The  eyes  begin  their  development  very  early  in  embryonic  life.  As  optic 
depressions  they  are  visible  even  before  the  closure  of  the  medullary  groove. 


Fore-brain  vesicle 


Lens  area-S 


Optic  vesicle   ' 


Surface  ectoderm 


Optic  vesicle 


FiG-  373. — Section  through  head  of  chick  of  two  days'  incubation.  (Duval.)  The 
formation  of  the  optic  vesicle  and  stalk  api)cars  to  be  somewhat  more  advanced  on  the 
left  than  on  the  right. 


As  a  result  of  the  closure  of  this  groove,  the  optic  dejjressions  are  transformed 
into  the  optic  vesicles.  The  conned  ion  between  vesicle  and  brain  now  becomes 
narrowed  so  that  the  two  are  connected  only  by  the  thin  optic  stalk.  The 
surface  of  the  optic  vesicle  becomes  firndy  adiicrciit  to  the  epidermis  and  as  a 


570 


THE  ORGANS 


result  of  proliferation  of  ectodermic  cells  at  this  point  is  pushed  inward 
(invaginated),  forming  the  optic  cup.  The  invagination  of  the  optic  vesicle 
extends  also  to  the  stalk,  the  sulcus  in  the  latter  being  known  as  the  chorioid 


Fore-brain 


Lens  invagination  -  - 


Optic  vesicle  ' 


Lens  invagination 


'  Optic  vesicle 
Fig.  374. — Section  through  head  of  chick  of  three  days'  incubation.     (Duval.) 

fissure.  The  latter  serves  for  the  introduction  of  mesenchyme,  and  the  develop- 
ment of  the  hyaloid  retinal  artery.  Three  distinct  parts  may  now  be  distin- 
guished in  the  developing  eye,  which  at  this  stage  is  known  as  the  secondary 


Fore-brain 


Lens  vesicle 


Optic  cup. 


Fig.  375. — Showing  somewhat  later  stage  in  development  of  optic  cup  and  lens 
than  is  shown  in  Fig.  374.     (Duval.) 

optic  vesicle:  (a)  The  proliferating  epidermis  which  is  to  form  the  lens;  (b)  the 
more  superficial  of  the  invaginated  layers  which  is  to  become  the  retina;  and 
(c)  the  surrounding  mesodermic  tissue  from  which  the  outer  coats  of  the  eye 
are  to  develop. 


TECHNIC 

(i)  For  the  study  of  the  general  structures  of  the  eyeball  the  eye  of  some  large 
animal,  such  as  an  ox,  is  most  suitable.     Fix  the  eye  for  about  a  week  in  ten- 


THE  ORGANS  OF  SPECL\L  SENSE 


571 


per-cent.  formalin.  Then  wash  in  water  and  bisect  the  eye  in  such  a  manner 
that  the  knife  passes  through  the  optic-nerve  entrance  and  the  centre  of  the 
cornea.  The  hah"  eye  should  now  be  placed  in  a  dish  of  water  and  the  structures 
shown  in  Fig.  358  identified  with  the  naked  eye  or  dissecting  lens.  On  removing 
the  vitreous  and  retina,  the  pigmented  epithelium  of  the  latter  usually  remains 
attached  to  the  chorioid  from  which  it  may  be  scraped  and  examined  in  water  or 
mounted  in  glycerin.  In  removing  the  lens  note  the  lens  capsule  and  the  sus- 
pensory ligament.  The  lens  may  be  picked  to  pieces  with  the  forceps,  and  a 
small  piece,  after  further  teasing  with  needles,  examined  in  water  or  mounted 
in  glycerin  or  eosin-glycerin.  The  retinal  surface  of  the  chorioid  shows  the 
iridescent  membrane  of  Bruch.  By  placing  a  piece  of  the  chorioid,  membrane-of- 
Bruch-side  down,  over  the  tip  of  the  finger  and  gently  scraping  with  a  knife  in 


Conjunctival  epithelium 


Vitreus 


Lens  vesicle  '      sir-i       j—jij      .      -      -  p^^a   ^-j:     /-,   ,  •      ^  ,, 

Q.ffl      /-*7  •-    -     -     "  -  F^i  /Cn      fptic  stalk 

Retina  (inner  layer 
of  optic  cup) 


Pigmented  layer  of  retina  .  _  . 
(outer  layer  of  optic  cup) 

Fig.  376. — Diagram  of  developing  lens  and  optic  cup.  (Duval.)  The  cells  of  the 
inner  wall  of  the  lens  vesicle  have  begun  to  elongate  to  form  lens  fibres.  The  epithelium 
over  the  lens  is  the  anlage  of  the  corneal  epithelium.  The  mesodermal  tissue  between 
the  latter  and  the  anterior  wall  of  the  lens  vesicle  is  the  anlage  of  the  substantia  propria 
comese. 


the  direction  of  the  larger  vessels,  the  latter  may  be  distinctly  seen.  By  now 
staining  the  piece  lightly  with  hajmatoxjdin  and  strongly  with  eosin,  clearing  in 
oil  or  origanum  and  mounting  in  balsam,  the  choriocapillaris  and  the  layer  of 
straight  vessels  become  distinctly  visible  with  the  low-power  lens.  In  removing 
the  chorioid  note  the  close  attachment  of  the  latter  to  the  sclera,  this  being  due 
to  the  intimate  association  of  the  fibres  of  the  lamina  suprachorioidea  and  of  the 
lamina  fusca.  If  the  brown  shreds  attached  to  the  inner  side  of  the  sclera  be 
examined,  the  pigmented  connective-tissue  cells  of  the  sclera  can  be  seen. 

(2)  For  the  study  of  the  finer  structure  of  the  coats  of  the  eye,  a  human  eye 
if  it  is  possible  to  obtain  one,  if  not,  an  eye  from  one  of  the  lower  animals,  should 
be  fixed  in  formalin-Miiller's  fluid  (technic  5,  p.  7)  and  hardened  in  alcohol.  (A 
few  drops  of  strong  formalin  injected  by  means  of  a  hypodermic  needle  directly 
into  the  vitreous  often  improves  the  fixation.)  The  eye  should  next  be  divided 
into  quadrants  by  first  carrying  the  knife  through  the  middle  of  the  cornea  and  of 
the  optic-nerve  entrance,  and  then  dividing  each  half  into  an  anterior  and  a 
posterior  half.  Block  in  celloidin,  cut  the  following  sections,  and  stain  with 
haematoxylin-eosin  (technic  i,  p.  20). 

(a)  Section  through  the  sclero-corneal  junction,  including  the  ora  serrata. 


572  THE  ORGANS 

ciliary  body,  iris,  and  lens.  Before  attempting  to  cut  this  section  almost  all  of 
the  lens  should  be  picked  out  of  the  block,  leaving  only  a  thin  anterior  and 
lateral  rim  attached  to  the  capsule  and  suspensory  ligament.  The  block  should 
then  be  so  clamped  to  the  microtome  that  the  lens  is  the  last  part  of  the  block 
to  be  cut.  The  above  precautions  are  necessary  on  account  of  the  density  of  the 
lens,  making  it  difficult  to  cut. 

(b)  Section  through  the  postero-lateral  portion  of  the  eyeball  to  show  struc- 
ture of  sclera,  chorioid,  and  retina.  This  section  should  be  as  thin  as  possible 
and  perpendicular  to  the  surface. 

(c)  Section  through  the  entrance  of  the  optic  nerve.  Haematoxylin-picro- 
acid-fuchsin  also  makes  a  good  stain  for  this  section.  It  is  instructive  in  cutting 
the  eye  to  cut  a  small  segment  from  the  optic  nerve  and  to  block  it  with  the  optic- 
nerve  entrance  material  in  such  a  manner  that  it  is  cut  transversely.  In  this  way 
both  longitudinal  and  transverse  sections  of  the  optic  nerve  appear  in  the  same 
section. 

(d)  For  the  study  of  the  neurone  relations  of  the  retina,  material  must  be 
treated  by  one  of  the  Golgi  methods  (page  35). 

(4)  The  connective-tissue  cells  and  cell  spaces  of  the  cornea  may  be  demon- 
strated by  means  of  technics  8  and  9,  page  97. 

(5)  The  different  parts  of  the  lacrymal  apparatus  may  be  studied  by  fixing 
material  in  formalin-Miiller's  fluid  and  staining  sections  in  haematoxylin-eosin. 

(6)  The  Eyelid.  An  upper  eyelid,  human  if  possible,  should  be  carefully 
pinned  out  on  cork,  skin  side  down,  and  fixed  in  formalin-Miiller's  fluid.  Vertical 
sections  should  be  stained  with  haematoxylin-eosin  or  with  hsematoxylin-picro- 
acid-fuchsin. 

The  Organ  of  Hearing 

The  organ  of  hearing  comprises  the  external  ear,  the  middle  ear, 
and  the  internal  ear. 

The  External  Ear 

The  external  ear  consists  of  the  pinna  or  auricle,  the  external 
auditory  canal,  and  the  outer  surface  of  the  tympanic  membrane. 

The  piitna  consists  of  a  framework  of  elastic  cartilage  embedded 
in  connective  tissue  and  covered  by  skin.  The  latter  is  thin  and  con- 
tains hairs,  sebaceous  glands,  and  sweat  glands. 

The  external  auditory  canal  consists  of  an  outer  cartilaginous  por- 
tion and  an  inner  bony  portion.  Both  are  lined  with  skin  continuous 
with  that  of  the  surface  of  the  pinna.  In  the  cartilaginous  portion  of 
the  canal  the  skin  is  thick  and  the  papillae  are  small.  Hair,  sebaceous 
glands,  and  large  coiled  glands  {ceruminous  glands)  are  present.  The 
last  named  resemble  the  glands  of  Mall  (page  568)  and  are  probably 
modified  sweat  glands.     Their  cells  contain  numerous  fat  droplets  and 


THE  ORGANS  OF  SPECT.\L  SENSE  573 

pigment  granules.  They  have  long  narrow  ducts  lined  with  a  two- 
layered  epithelium.  In  children  these  ducts  open  into  the  hair 
follicles;  in  the  adult  they  open  on  the  surface  near  the  hair  follicles. 
The  secretion  of  these  glands  plus  desquamated  epithelium  consti- 
tutes the  ear  wax.  In  the  bony  portion  of  the  canal  the  skin  is  thin, 
free  from  glands  and  hair,  and  firmly  adherent  to  the  periosteum. 

The  tympanic  membrane  (ear  drum)  separates  the  external  ear 
from  the  middle  ear.  It  consists  of  three  layers:  a  middle  layer  or 
substantia  propria,  an  outer  layer  continuous  with  the  skin  of  the 
external  ear,  and  an  inner  layer  continuous  with  the  mucous  mem- 
brane of  the  middle  ear. 

The  substantia  propria  consists  of  closely  woven  connective-tissue 
fibres,  the  outer  fibres  having  a  radial  direction  from  the  head  of 
the  malleus,  the  inner  fibres  having  a  concentric  arrangement  and 
being  best  developed  near  the  periphery. 

The  outer  layer  of  the  tympanic  membrane  is  skin,  consisting  of 
epidermis  and  of  a  thin  non-papillated  corium,  excepting  over  the 
manubrium  of  the  malleus,  where  the  skin  is  thicker  and  papillated. 

The  inner  layer  is  mucous  membrane  and  consists  of  a  stroma  of 
fibro-elastic  tissue  covered  with  a  single  layer  of  low  epithelial  cells. 

Blood-vessels. — Blood  is  supplied  to  the  tympanic  membrane  by 
two  sets  of  vessels,  an  external  set  derived  from  the  vessels  of  the 
external  auditory  meatus  and  an  internal  set  from  the  vessels  of  the 
middle  ear.  These  give  rise  to  capillary  networks  in  the  skin  and 
mucous  membrane,  respectively,  and  anastomose  by  means  of  perfo- 
rating branches  at  the  periphery  of  the  membrane.  From  the  capil- 
laries the  blood  passes  into  two  sets  of  small  veins,  one  extending 
around  the  periphery  of  the  membrane,  the  other  following  the  handle 
of  the  malleus. 

Lymphatics. — -These  follow  in  general  the  course  of  the  blood- 
vessels.    They  are  most  numerous  in  the  outer  layer. 

Nerves. — The  larger  nerves  run  in  the  substantia  propria.  From 
these,  branches  pass  to  the  skin  and  mucous  membrane,  beneath  the 
surfaces  of  which  they  form  i)lexuses  of  fme  fibres. 

The  Middle  Ear 

The  middle  ear  or  lympanum  is  a  small  chamber  separate<l  from 
the  external  ear  by  the  tympanic  membrane  and  communicating  with 
the  pharynx  by  means  (^f  the  Eustachian  tube.     Its  walls  are  formed 


574  THE  ORGANS 

by  the  surrounding  bony  structures  covered  b}^  periosteum.  It  is 
lined  with  mucous  membrane  and  contains  the  ear  ossicles  and  their 
ligamentous  and  muscular  attachments.  The  epithehum  is  of  the 
simple  low  cuboidal  tj^e.  In  places  it  may  be  cihated  and  not  infre- 
quently assumes  a  pseudostratified  character  mth  two  layers  of 
nuclei.  Beneath  the  epithelium  is  a  thin  stroma  which  contains  some 
diffuse  l3aiiphoid  tissue  and  blends  with  the  dense  underlying  perios- 
teum. SmaU  tubular  glands  are  usually  present,  especially  near  the 
opening  of  the  Eustachian  tube. 

The  fenestra  rotunda  is  covered  b}'  the  secondary  tpiipanic  mem- 
brane. This  consists  of  a  central  lamina  of  connective  tissue  covered 
on  its  tympanic  side  by  part  of  the  mucous  membrane  of  that  cham- 
ber, on  the  opposite  side  by  a  single  layer  of  endothehum. 

The  ossicles  are  composed  of  bone  tissue  arranged  in  the  usual 
systems  of  lamellae.  The  stapes  alone  contains  a  marrow  cavity. 
Over  their  articular  surfaces  the  ossicles  are  covered  b}"  hyahne 
cartilage. 

The  Eustachian  Tube. — This  is  a  partly  bony,  partly  cartilaginous 
canal  hned  with  mucous  membrane.  The  epithehum  of  the  latter  is 
of  the  stratified  columnar  cihated  variety  consisting  of  two  layers  of 
cells.  In  the  bony  portion  of  the  tube  the  stroma  is  small  in  amount 
and  intimately  connected  \\T[th  the  periosteum.  In  the  cartilaginous 
portion  the  stroma  is  thicker  and  contains,  especially  near  the  pharyn- 
geal opening,  lymphoid  tissue  and  simple  tubular  mucous  glands. 

The  Internal  Ear 

The  internal  ear  consists  of  a  complex  series  of  connected  bony 
walled  chambers  and  passages  containing  a  similar-shaped  series  of 
membranous  sacs  and  tubules.  These  are  known,  respectively,  as  the 
osseous  labyrinth  and  the  me?nbranous  labyrinth.  Between  the  two  is 
a  lymph  space,  which  contains  the  so-called  perilymph,  while  within 
the  membranous  lab3Tinth  is  a  similar  fluid,  the  endolymph. 

The  bony  labyrinth  consists  of  a  central  chamber,  the  vestibule, 
from  which  are  given  off  the  three  semicircular  canals  and  the  cochlea. 
The  vestibule  is  separated  from  the  middle  ear  by  a  plate  of  bone  in 
which  are  two  openings,  the  fenestra  ovalis  and  the  fenestra  rotunda. 
Just  after  leaving  the  vestibule  each  canal  presents  a  dilatation,  the 
ampulla.  As  each  canal  has  a  return  opening  into  the  vestibule  and 
as  the  anterior  and  posterior  canals  have  a  common  return  opening 


THE  ORGANS  OF  SPECI.\L  SENSE 


575 


Ampjilla6f 


(the  canalis  communis),  there  are  five  openings  from  the  vestibule 
into  the  semicircular  canals  (Fig.  377).  The  bony  labyrinth  is  lined 
with  periosteum,  covered  by  a  single  layer  of  endothelial  cells. 

The  Vestibule  and  the  Semicircular  Canals.^In  the  vestibule 
the  membranous  labyrinth  is  subdi\dded  into  two  chambers,  the  sac- 
cule and  the  utricle,  which  are  connected  by  the  utriculosaccular  duct. 
From  the  latter  is  given  off  the  endolymphatic  duct  which  communi- 
cates, through  the  aqueduct  of  the  vestibule,  with  a  subdural  lymph 
space,  the  endolymphatic  sac.  The  saccule  opens  by  means  of  the 
ductus  reuniens  into  the  cochlea, 
while  the  utricle  opens  into  the 
ampullae  of  the  semicircular 
canals.  The  saccule  and  utricle 
only  partly  fill  the  vestibule, 
the  remaining  space,  crossed  by 
fibrous  bands  and  fined  with 
endothefium,  constituting  the 
perilymphatic  space. 

Saccule  and  Utricle. — The 
walls  of  the  saccule  and  of  the 
utricle  consist  of  fine  fibro- 
elastic  tissue  supporting  a  thin 
basement    membrane,    upon 

which  rests  a  single  layer  of  low  epithelial  cells.  In  the  wall 
of  each  chamber  is  an  area  of  special  nerve  distribution,  the 
macula  acustica.  ^  Here  the  epithefium  changes  to  high  columnar  and 
consists  of  two  kinds  of  cells,  sustentacular  and  neuro-epithelial. 
The  sustentacular  cells  are  long,  irregular,  nucleated  cyhnders,  narrow 
in  the  middle,  widened  at  each  end,  the  outer  end  being  frequently 
split  and  resting  upon  the  basement  membrane.  The  neuro-epithelial 
cells  or  "hair  cells"  are  short  cylinders  which  extend  only  about  half- 
way through  the  epithelium.  The  basal  end  of  the  cell  is  the  larger 
and  contains  the  oval  nucleus.  The  surface  of  the  cell  is  provided 
with  a  cuticular  margin  from  which  project  several  long  hair-like 
processes,  the  auditory  hairs.  Small  crystals  of  calcium  carbonate  are 
found  on  the  surfaces  of  the  hair  cells,  rhcse  are  known  as  otoliths 
and  are  embedded  in  a  soft  substance,  the  otolithic  membrane.  The 
hair  cells  are  the  neuro-epithelial  end-organs  of  the  vestibular  divi- 
sion of  the  auditory  nerve  and  are,  therefore,  closely  associated  with 
the  nerve  fibres.     The  latter  on  piercing  the  basement  membrane 


Fig. 


-The    Bony   Labyrinth. 
(Heitzmann.j 


576 


THE  ORGANS 


lose  their  medullary  sheaths  and  split  up  into  several  small  branches, 
which  form  a  horizontal  plexus  between  the  basement  membrane  and 
the  bases  of  the  hair  cells.  From  this  plexus  are  given  off  fibrils 
which  end  freely  between  the  hair  cells. 

Semicircular  Canals. — The  walls  of  the  semicircular  canals  are 
similar  in  structure  to  the  walls  of  the  saccule  and  utricle;  they  also 
bear  a  similar  relation  to  the  walls  of  the  bony  canal.  Along  the  con- 
cavity of  each  canal  the  epithelium  is  somewhat  higher,  forming  the 


Fig.  378. — Diagram  of  the  Perilymphatic  and  Endolymphatic  Spaces  of  the  Inner 
Ear.  (Testut.)  Endolymphatic  spaces  in  gray;  perilymphatic  spaces  in  black,  i, 
Utricle;  2,  saccule;  3,  semicircular  canals;  4,  cochlear  canal;  5,  endolymphatic  duct;  6, 
subdural  endolymphatic  sac;  7,  canalis  reuniens;  8,  scala  tympani;  9,  scala  vestibuU; 
ID,  their  union  at  the  heHcotrema;  11,  aqueduct  of  the  vestibule;  12,  aqueduct  of  the 
cochlea;  13,  periosteum;  14,  dura  mater;  15,  stapes  in  fenestra  ovalis;  16,  fenestra 
rotunda  and  secondary  tympanic  membrane. 

raphe.  In  each  ampulla  is  a  crista  acustica,  the  structure  of  which  is 
similar  to  that  of  the  maculae  of  the  saccule  and  utricle.  With  the 
adjoining  high  columnar  cells,  this  forms  the  so-called  semilunar  fold. 
As  in  the  case  of  the  maculae  the  hair  cells  have  otoliths  upon  their 
surfaces,  the  otolithic  membrane  here  forming  a  sort  of  dome  over  the 
hair  cells  known  as  the  cupula. 

The  Cochlea. — The  bony  cochlea  consists  of  a  conical  axis,  the 
modiolus,  around  which  winds  a  spiral  bony  canal.  This  canal  in 
man  makes  about  two  and  one-half  turns,  ending  at  the  rounded  tip 
of  the  cochlea  or  cupola.     Projecting  from  the  modiolus  partly  across 


THE  ORGAXS  OF  SPECL\L  SENSE 


577 


the  bony  canal  of  the  cochlea  is  a  plate  of  bone,  the  bony  spiral  lamina 
(Fig.  381,  .r).  This  follows  the  spiral  turns  of  the  cochlea,  ending  at 
the  cupola  in  a  hook-shaped  process,  the  hamulus.     Along  the  outer 


Fig.  379. — Diagram  of  the  Right  JMembranous  Labyrinth.  (Teslut.)  i,  Utricle;  2 
superior  semicircular  canal;  3,  posterior  semicircular  canal;  4,  external  semicircular 
canal;  5,  saccule;  6,  endolj-mphatic  duct;  7  and  7',  canals  connecting  utricle  and  saccule 
respectively  \\'ith  the  endolymphatic  duct;  8,  endolymphatic  sac;  9,  cochlear  duct;  9', 
its  vestibular  cul-de-sac;  9",  its  terminal  cul-de-sac;  10,  canalis  reuniens. 


IB- 


Fig.  380.- — The  Membranous  Labyrinth  from  the  Right  Internal  Ear  of  a  Human 
Embryo  at  the  Fifth  Month;  seen  from  the  Medial  Side.  (After  Rctzius,  from  Barker.) 
1-5,  Utricle;  2,  utricular  recess;  3,  macula  acustica  of  utricle;  4,  posterior  sinus;  5,  supe- 
rior sinus;  6,  7,  8,  superior,  lateral,  and  [josterior  ampullae;  9,  10,  11,  superior,  posterior, 
and  lateral  semicircular  canals;  12,  widened  mouth  of  lateral  semicircular  canal  open- 
ing into  the  utricle;  13,  saccule;  14,  macula  acustica  of  the  saccule;  15,  endolymphatic 
duct;  16,  utriculo-saccular  duct;  17,  ductus  reuniens;  18,  vestibular  cul-de-sac  of  coch- 
lear duct;  19,  cochlear  duct;  20,  facial  nerve;  21-24,  auditory  nerve;  21,  its  vestibular 
branch;  22,  saccular  branch;  23,  branch  to  inferior  ami)ulla;  24,  cochlear  branch;  25, 
distribution  of  cochlear  branch  within  the  bony  spiral  lamina. 

side  of  the  canal,  opposite  the  bony  spiral  lamina,  is  a  projection  of 
thickened  periosteum,  the  spiral  ligament  (Fig.  381,  h).  A  con- 
nective tissue  membrane,  the  membranous  spiral  lamina  (Fig.  381,  s). 

37 


578 


THE  ORGANS 


crosses  the  space  intervening  between  the  spiral  Hgament  and  the 
bony  spiral  lamina,  thus  completely  dividing  the  bony  canal  of  the 
cochlea  into  two  parts,  an  upper,  scala  vestihuli  (Fig.  381,  I)  and  a 
lower,  scala  tympani  (Fig.  381,  k).  These  are  perilymphatic  spaces, 
the  scala  vestibuli  communicating  with  the  perilymph  space  of  the 
vestibule,  the  scala  tympani  communicating  with  the  perivascular 


Fig.  381. — Section  through  a  Single  Turn  of  the  Cochlea  of  a  Guinea-pig.  (Bohm 
and  von  Davidoff.)  a,  Bone  of  cochlea;  /,  scala  vestibuli,  Dc,  scala  media  or  cochlear 
duct;  k,  scala  tympani;  5, membrane  of  Reissner;  J,membrana  tectoria  or  membrane  of 
Corti;  /,  spiral  prominence;  g,  organ  of  Corti;  h.  spiral  ligament;  i,  basilar  membrane 
(outer  portion — zona  pectinata — covered  by  cells  of  Claudius);  z,  stria  vascularis;  v, 
external  spiral  sulcus;  r,  crista  basilaris;  s,  membranous  spiral  lamina;  x,  bony  spiral 
lamina;  m,  spiral  limbus;  n,  internal  spiral  sulcus;  0,  meduUated  peripheral  processes 
(dendrites)  of  cells  of  spiral  ganglion  passing  to  the  organ  of  Corti;  p,  spiral  ganglion; 
q,  blood-vessel. 


lymph  spaces  of  the  veins  of  the  cochlear  duct.  The  scala  vestibuli 
and  the  scala  tympani  communicate  with  each  other  in  the  cupola  by 
means  of  a  minute  canal,  the  helicotrema. 

The  Cochlear  Duct  {Membranous  Cochlea  or  Scala  Media). — 
This  is  a  narrow,  membranous  tube  lying  near  the  middle  of  the 
bony  cochlear  canal  and  following  its  spiral  turns  from  the  vestibule, 
where  it  is  connected  with  the  saccule  through  the  canalis  reuniens, 


THE  ORGANS  OF  SPECI.AJL  SENSE  579 

to  its  blind  ending  in  the  cupola.  It  is  triangular  in  shape  on  trans- 
verse section,  thus  allowing  a  division  of  its  walls  into  upper,  outer, 
and  lower  (Fig.  381,  Dc). 

The  upper  or  vestibular  wall  is  formed  by  the  thin  membrane  of 
Reissner  (Fig.  381,  h)  which  separates  the  cochlear  duct  from  the 
scala  vestibuli.  The  membrane  consists  of  a  thin  central  lamina  of 
connective  tissue  covered  on  its  vestibular  side  by  the  vestibular 
endothelium,  on  its  cochlear  side  by  the  epithelium  of  the  cochlea. 

The  cuter  wall  of  the  cochlear  duct  is  formed  by  the  spiral  liga- 
ment, which  is  a  thickening  of  the  periosteum.  The  outer  part  of  the 
spiral  ligament  consists  of  dense  fibrous  tissue,  its  projecting  part  of 
more  loosely  arranged  tissue.  From  it,  two  folds  project  slightly 
into  the  duct.  One,  the  crista  hasilaris  (Fig.  381,  r),  serves  for  the 
attachment  of  the  membranous  spiral  lamina;  the  other,  the  spiral 
promhience  (Fig.  381,/),  contains  several  small  veins.  Between  the 
two  projections  is  a  depression,  the  external  spiral  sulcus  (Fig.  381,  v). 
That  part  of  the  spiral  ligament  between  the  spiral  prominence  and 
the  attachment  of  Reissner's  membrane  is  known  as  the  stria  vascu- 
laris (Fig.  381,  2).  It  is  lined  with  granular  cuboidal  epithelial  cells, 
which,  cwing  to  the  absence  of  a  basement  membrane,  are  not  sharply 
separated  from  the  underlying  connective  tissue.  For  this  reason  the 
capillaries  extend  somewhat  between  the  epithelial  cells,  giving  the 
unusual  appearance  of  a  vascular  epithelium. 

The  lower  or  tympanic  wall  of  the  cochlear  duct  has  an  extremely 
complex  structure.  Its  base  is  formed  by  the  already  mentioned 
bony  and  membranous  division-wall  between  the  scala  media  and  the 
scala  tympani  (bony  spiral  lamina  and  membranous  spiral  lamina). 

The  bony  spiral  lamina  has  been  described  (page  577). 

The  membranous  spiral  lamina  consists  of  a  substantia  propria  or 
Vjasilar  membrane,  its  tympanic  covering,  and  its  cochlear  covering. 

The  basilar  membrane  (Fig.  381)  is  a  connective-tissue  membrane 
composed  of  fine  straight  fibres  which  extend  from  the  bony  spiral 
lamina  to  the  spiral  Hgament.  Among  the  fibres  are  a  few  connective- 
tissue  cells.  On  either  side  of  the  fibre  layer  is  a  thin,  apparently 
structureless  membrane. 

The  tympanic  covering  oi  the  basilar  membrane  consists  of  a  thin 
layer  of  connective  tissue  -  an  extension  of  the  periosteum  of  the  spiral 
lamina — covered  over  by  a  single  layer  of  flat  endothelial  cells. 

The  cochlear  covering  of  the  basilar  membrane  is  epithelial.  Owing 
to  the  marked  difference  in  the  character  of  the  epithelium,  the  basilar 


580 


THE  ORGANS 


membrane  is  divided  into  an  outer  portion,  the  zona  pectinata  (Fig. 
381,  i)  and  an  inner  portion,  the  zona  tecta  (Fig.  381,  5).  The  epithe- 
hum  of  the  former  is  of  the  ordinary  columnar  type;  that  of  the  latter 
is  the  highly  differentiated  neuro-epithelium  of  Corti's  organ. 

The  Organ  of  Corti. — The  spiral  organ  or  the  organ  of  Corti  (Fig. 
381,  g,  and  Fig.  382)  is  a  neuro-epithelial  structure  running  the  entire 
length  of  the  cochlear  canal  with  the  exception  of  a  short  distance  at 
either  end.  It  rests  upon  the  membranous  portion  of  the  spiral 
lamina,  and  consists  of  a  complex  arrangement  of  four  different  kinds 


limhus 


itiemlraTM  tectoriw 


outer  hair -cells 


nervejibres 


inner  rod    vas    basilar         outer    cells  of  Deitsrs 
spifolc    membrane     'rod 


Fig.  382. — Semidiagrammatic  Representation  of  the  Organ  of  Corti  and  Adjacent 
Structures  (Merkel-Henle.)  a,  Cells  of  Hensen;  h,  cells  of  Claudius;  c,  internal  spiral 
sulcus;  X,  Nuel's  space.  The  nerve  fibres  (dendrites  of  cells  of  the  spiral  ganglion)  are 
seen  passing  to  Corti's  organ  through  openings  (foramina  nervosa)  in  the  bony  spiral 
lamina.  The  black  dots  represent  longitudinally-running  branches,  one  bundle  lying 
to  the  inner  side  of  the  inner  pillar,  a  second  just  to  the  outer  side  of  the  inner  pillar 
within  Corti's  tunnel,  the  third  beneath  the  outer  hair  cells. 


of  epithelial  cells.     These  are  known  as:  (i)  pillar  cells,  (2)  hair  cells, 
(3)  Deiter's  cells,  and  (4)  Hensen's  cells  (Fig.  352). 

(i)  The  pillar  cells  are  divided  into  outer  pillar  cells  and  inner 
pillar  cells.  They  are  sustentacular  in  character.  Each  cell  consists 
of  a  broad  curved  protoplasmic  base  which  contains  the  nucleus,  and 
of  a  long-drawn-out  shaft  or  pillar  which  probably  represents  a  highly 
specialized  cuticular  formation.  The  end  of  the  pillar  away  from  the 
base  is  known  as  the  head.  The  head  of  the  outer  pillar  presents  a 
convexity  on  its  inner  side,  which  fits  into  a  corresponding  concavity 
on  the  head  of  the  inner  pillar,  the  heads  of  opposite  pillars  thus 
"articulating"  with  each  other.  From  their  articulation  the  pillars 
diverge,  so  that  their  bases  which  rest  upon  the  basilar  membrane  are 


THE  ORGANS  OF  SPECIAL  SENSE  581 

widely  separated.  There  are  thus  formed  by  the  pillars  a  series  of 
arches  known  as  Corti's  arclies,  enclosing  a  triangular  canal,  Corti's 
tunnel.  This  canal  is  filled  with  a  gelatinous  substance  and  crossed 
by  dehcate  nerve  fibrils.  As  the  outer  pillar  cells  are  the  larger, 
they  are  fewer  in  number,  the  estimated  number  in  the  human  coch- 
lea being  forty-five  hundred  of  the  outer  cells  and  about  six  thousand 
of  the  inner  cells. 

(2)  The  hair  cells  or  auditory  cells  lie  on  either  side  of  the  arches 
of  Corti,  and  are  thus  divided  into  inner  hair  cells  and  outer  hair 
cells.  Both  inner  and  outer  hair  cells  are  short,  cyhndrical  dements 
which  do  not  extend  to  the  basilar  membrane.  Each  cell  ends  below 
in  a  point,  while  from  its  free  surface  are  given  oft'  a  number  of  fine 
stiff  hairs. 

The  inner  hair  cells  He  in  a  single  layer  against  the  inner  side  of 
the  inner  pillar  cells,  one  hair  cell  resting  upon  about  every  two 
pillars. 

The  outer  hair  cells  He  in  three  or  four  layers  to  the  outer  side  of 
the  outer  pillar  cells,  being  separated  from  one  another  by  susten- 
tacular  cells,  the  cells  of  Deiter,  so  that  no  two  hair  cells  come  in 
contact. 

(3)  Deiter 's  Cells  (Fig.  382).— These  like  the  pillar  cells  are  sus- 
tentacular.  Their  bases  rest  upon  the  basilar  membrane,  where  they 
form  a  continuous  layer.  Toward  the  surface  they  become  separated 
from  one  another  by  the  hair  cells.  The  long  slender  portions  of  the 
Deiter 's  cells,  which  pass  in  between  the  hair  cells,  are  known  as  pha- 
langeal  processes.  Between  the  innermost  of  the  outer  hair  cells  and 
the  cuter  pillar  is  a  space  known  as  NueVs  space  (Fig.  382,  :r). 

(4)  Hensen's  Cells  (Fig.  382,  a).— These  are  sustentacular  cells, 
which  form  about  eight  rows  to  the  outer  side  of  the  outermost 
Deiter 's  cells.  These  cells  form  the  outer  crest  of  Corti 's  organ  and 
consequently  have  a  somewhat  radial  disposition,  their  free  surfaces 
being  broad,  their  basal  ends  narrow.  They  decrease  in  height  from 
within  outward,  and  at  the  end  of  Corti 's  organ  become  continuous 
with  the  cells  of  Claudius  (Fig.  382,  b),  the  name  given  to  the  coch- 
lear epithelium  covering  the  basal  membrane  to  the  outer  side  of 
Corti 's  organ. 

The  phalangeal  processes  of  the  Deiter 's  cells  are  cemented  to- 
gether and  to  the  superficial  parts  of  the  outer  pillars  in  such  a  man- 
ner as  to  form  a  sort  of  cuticular  membrane,  the  lamina  reticularis, 
through  which  the  heads  of  the  outer  hair  cells  |)r()jc(t.     This  incm- 


582  THE  ORGANS 

brane  also  extends  out  as  a  cuticula  over  the  cells  of  Hensen  and  of 
Claudius. 

The  Membrana  Tectoria. — This  is  a  peculiar  membranous  struc- 
ture attached  to  a  projection  of  the  bony  spiral  lamina  known  as  the 
spiral  limbus  (Fig.  382),  the  concavity  beneath  its  attachment  being 
the  internal  spiral  sulcus  (Fig.  382,  c).  The  membrane  is  non-nucle- 
ated and  shows  fine  radial  striations.  It  bridges  over  the  internal 
spiral  sulcus  and  ends  in  a  thin  margin,  which  rests  upon  Corti's 
organ  just  at  the  outer  limit  of  the  outer  hair  cells. 

Blood-vessels. — The  arteries  consist  of  two  small  branches  of  the 
auditory — one  to  the  bony  labyrinth,  the  other  to  the  membranous 
labyrinth.  The  latter  divides  into  two  branches — a  vestibular  and  a 
cochlear.  The  vestibular  artery  accompanies  the  branches  of  the 
auditory  nerve  to  the  utricle,  saccule,  and  semicircular  canals.  It 
supplies  these  parts,  giving  rise  to  a  capillary  network,  which  is 
coarse  meshed  except  in  the  cristse  and  maculae,  where  the  meshes  are 
fine.  The  cochlear  artery  also  starts  out  in  company  with  the  audi- 
tory nerve,  but  accompanies  it  only  to  the  first  turn  of  the  cochlea. 
Here  it  enters  the  modiolus  where  it  gives  off  several  much  coiled 
branches,  the  glomerular  arteries  of  the  cochlea.  Branches  from 
these  pierce  the  vestibular  part  of  the  osseous  spiral  lamina  and 
supply  the  various  structures  of  the  cochlear  duct.  The  veins  ac- 
company the  arteries,  but  reach  the  axis  of  the  modiolus  through 
foramina  in  the  tympanic  part  of  the  bony  spiral  lamina. 

Lymphatics. — The  scala  media  contains  endolymph  and  is  in 
communication  with  the  subdural  lymph  spaces  by  means  of  the  en- 
dolymphatic duct,  the  endolymphatic  sac,  and  minute  lymph  chan- 
nels connecting  the  latter  with  the  subdural  spaces.  The  perilymph 
spaces — scala  tympani  and  scala  vestibuli — are  connected  with  the 
pial  lymph  spaces  by  means  of  the  perilymphatic  duct.  Lymph 
spaces  also  surround  the  vessels  and  nerves.  These  empty  into  the 
pial  lymphatics. 

Nerves. — The  vestibular  branch  of  the  auditory  nerve  divides 
into  branches  which  supply  the  saccule,  utricle,  and  semicircular 
canals,  where  they  end  in  the  maculae  and  cristae  as  described  on 
page  575.  The  ganglion  of  the  vestibular  branch  is  situated  in  the 
internal  auditory  meatus.  The  cochlear  branch  of  the  auditory 
nerve  enters  the  axis  of  the  modiolus,  where  it  divides  into  a  number 
of  branches  which  pass  up  through  its  central  axis.     From  these, 


THE  ORGANS  OF  SPECI.\L  SENSE  583 

numerous  fibres  radiate  to  the  bony  spiral  laminse,  in  the  bases  of 
which  they  enter  the  spiral  gangUa  (Fig.  381,  p). 

The  cells  of  the  spiral  ganglia  are  peculiar,  in  that  while  of  the 
same  general  type  as  the  spinal  ganglion  cell  they  maintain  their 
embryonic  bipolar  condition  (see  page  419)  throughout  life.  Their 
axones  follow  the  already  described  course  through  the  modiolus  and 
thence  through  the  internal  auditory  meatus  to  their  terminal  nuclei 
in  the  medulla  (see  page  493).  Their  dendrites  become  medul- 
lated  like  the  dendrites  of  the  spinal  ganglion  cells  and  pass  outward 
in  bundles  in  the  bony  spiral  lamina  (Fig  381,  0,  and  Fig.  382). 
From  these  are  given  off  branches  which  enter  the  tympanic  portion 
of  the  lamina,  where  they  lose  their  medullary  sheaths  and  pass 
through  the  foramina  nervosa  (minute  canals  in  the  tympanic  part 
of  the  spiral  lamina)  to  their  terminations  in  the  organ  of  Corti. 
In  the  latter  the  fibres  run  in  three  bundles  parallel  to  Corti 's  tun- 
nel. One  bundle  lies  just  inside  the  inner  pillar  beneath  the  inner 
row  of  hair  cells  (Fig.  382).  A  second  bundle  runs  in  the  tunnel  to 
the  outer  side  of  the  inner  pillar  (Fig.  382).  The  third  bundle  crosses 
the  tunnel  (tunnel-fibres)  and  turns  at  right  angles  to  run  between 
the  cells  of  Deiter  beneath  the  outer  hair  cells  (Fig.  382).  From  all 
of  these  bundles  of  fibres  are  given  off  delicate  terminals  which  end 
on  the  hair  cells.  (For  details  of  acoustic  tract  see  pp.  475,  476, 
and  493.) 

Development  of  the  Ear 

The  essential  auditoty  part  of  the  organ  of  hearing,  the  membranous  laby- 
rinth, is  of  ectodermic  origin.  This  first  appears  as  a  thickening  followed  by 
an  invagination  of  the  surface  ectoderm  in  the  region  of  the  posterior  cerebral 
vesicle.  This  is  known  as  the  auditory  pit.  By  closure  of  the  lips  of  this  pit 
and  growth  of  the  surrounding  mesodcrmic  tissue  is  formed  the  otic  vesicle  or 
otocyst,  which  is  completely  separated  from  the  surface  ectoderm.  Diver- 
ticula soon  appear  passing  of?  from  the  otic  vesicle.  These  are  three  in  number 
and  correspond  respectively  to  the  future  endolymphatic  duct,  the  cochlear 
duct  and  the  membranous  semicircular  canals.  Within  the  saccule,  utricle, 
and  ampullae  special  differentiations  of  the  lining  epithelium  give  rise  to  the 
maculie  and  crista;  acusticae.  Of  the  cochlear  duct  the  upper  and  lateral  walls 
become  thinned  to  form  Reissner's  membrane  and  the  epithelium  of  the  outer 
wall,  while  the  lower  wall  becomes  the  basilar  membrane,  its  epithelium  under- 
going an  elaborate  specialization  to  form  the  organ  Corti. 

Of  the  cochlea,  only  the  membranous  cochlear  duct  develops  from  the  otic 
vesicle;  the  scala  vestibuli,  scala  tympani,  and  bony  cochlea  developing  from 
the  surrounding  mcsoficrm.     The  mesodcrmic  connective  tissue  at  first  com- 


584  THE  ORGANS 

pletely  fills  in  the  space  between  the  cochlear  duct  and  the  bony  canal.  Ab- 
sorption of  this  tissue  takes  place,  resulting  in  formation  of  the  scala  tympani 
and  scala  vestibuli. 

During  the  differentiation  of  the  above  parts  a  constriction  appears  in  the 
body  of  the  primitive  otic  vesicle.  This  results  in  the  incomplete  septum 
which  divides  the  utricle  from  the  saccule. 

The  middle  ear  is  formed  from  the  upper  segment  of  the  pharyngeal 
groove,  the  lower  segment  giving  rise  to  the  Eustachian  tube. 

The  external  ear  is  developed  from  the  ectoderm  of  the  first  branchial  cleft 
and  adjacent  branchial  arches.  The  tympanic  membrane  is  formed  from  the 
mesoderm  of  the  first  branchial  arch,  its  outer  covering  being  of  ectodermic,  its 
inner  of  entodermic  origin. 

TECHNIC 

(i)  For  the  study  of  the  general  structure  of  the  pinna  and  walls  of  the  exter- 
nal auditory  meatus,  material  may  be  fixed  in  formalin-Miiller's  fluid  (technic  5, 
p.  7)  and  sections  stained  with  haematoxylin-eosin  (technic  i,  p.  20).  In  sections 
of  the  wall  ot  the  cartilaginous  meatus  the  ceruminous  glands  may  be  studied, 
material  from  children  and  from  new-born  infants  furnishing  the  best  demon- 
strations of  these  glands. 

(2)  For  the  study  of  the  inner  ear  the  guinea-pig  is  most  satisfactory  on 
account  of  the  ease  with  which  the  parts  may  be  removed.  Remove  the  cochlea 
of  a  guinea-pig  with  as  much  as  possible  of  the  vestibule  and  semicircular  canals 
and  fix  in  Flemming's  fluid  (technic  7,  p.  7).  A  small  opening  should  be  made 
in  the  first  turn  of  the  cochlea  in  order  to  allow  the  fixative  to  enter  the  canal. 
After  forty-eight  hours  the  cochlea  is  removed  from  the  fixative  and  hardened  in 
graded  alcohols  (page  8).  The  bone  is  next  decalcified,  either  by  one  of  the 
methods  mentioned  on  page  10  or  in  saturated  alcoholic  solution  of  picric  acid. 
If  one  of  the  aqueous  decalcifying  fluids  is  used,  care  must  be  taken  to  carry  the 
material  through  graded  alcohols.  Embed  in  celloidin  or  paraffin,  cut  sections 
through  the  long  axis  of  the  modiolus,  through  the  utricle  and  saccule,  and 
through  the  semicircular  canals.  Stain  with  haematoxylin-eosin  and  mount  in 
balsam. 

(3)  The  neurone  relations  of  the  cristse,  maculae,  and  cochlear  duct  can  be 
demonstrated  only  by  means  of  the  Golgi  method.  The  ear  of  a  new-born  mouse 
or  guinea-pig  furnishes  good  material.  The  cochlea  together  with  some  of  the 
base  of  the  skull  should  be  removed  and  treated  by  the  Golgi  rapid  method  (page 
SS)-  Sections  should  be  thick  and  must  of  course  be  cut  through  undecalcified 
bone.     Good  results  are  difficult  to  obtain. 

The  Organ  of  Smell 

The  olfactory  organ  consists  of  the  olfactory  portion  of  the  nasal 
mucosa.  In  this  connection  it  is,  however,  convenient  to  describe 
briefly  the  olfactory  bulb  and  the  olfactory  tract. 

The  Olfactory  Mucosa. — This  has  been  described  (page  299).     The 


THE  ORGANS  OF  SPECIAL  SENSE 


585 


peculiar  olfactory  cells  there  described  are  not  neuro-epithelium  but 
are  analogs  of  the  spinal  ganghon  cell,  being  the  only  example  in  man 
of  the  peripherally  placed  ganglion  cell  found  in  certain  lower  animals. 
Each  cell  sends  to  the  surface  a  short  dendrite  which  ends  in  several 
short,  stiff,  hair-like  processes.  From  its  opposite  end  each  cell 
gives  off  a  longer  centrally  directed  process  (axone),  which  as  a  fibre 
of  one  of  the  olfactory  nerves  passes  through  the  cribriform  plate 
of  the  ethmoid  (Fig.  383,  ethm)  to  its  terminal  nucleus  in  the  olfac- 
tory bulb  (Fig.  383). 

The  Olfactory  Bidh. — This  is  a  somewhat  rudimentary  structure 
analogous  to  the  much  more  prominent  olfactory  brain  lobe  of  some 


Fig.  383. — Diagram  of  Structure  of  Olfactory  jVIucosa  and  Olfactory  Bulb.  (Rani6n 
y  Cajal.)  be,  Bipolar  cells  of  olfactory  mucosa;  sm,  submucosa;  ethm,  cribriform  plate 
of  ethmoid;  a,  layer  of  olfactory  fibres;  og,  olfactory  glomeruli;  me,  mitral  cells;  ep, 
epithelium  of  olfactory  ventricle. 

of  the  lower  animals.  It  consists  of  both  gray  matter  and  white 
matter  arranged  in  six  fairly  distinct  layers.  These  from  below 
upward  are  as  follows:  (a)  Thelayer  of  olfactory  fibres;  (6)  the  layer 
of  glomeruH;  (c)  the  molecular  layer;  {d)  the  layer  of  mitral  cells; 
{e)  the  granule  layer;  if)  the  layer  of  longitudinal  fibre  bundles. 
Through  the  centre  of  the  last-named  layer  runs  a  band  of  neuroglia 
which  represents  the  obliterated  lumen  of  the  embryonal  lobe.  The 
relations  of  these  layers  to  the  olfactory  neurone  system  are  as  fellows: 


586  THE  ORGANS 

The  layer  cf  olfactory  fibres  (Fig.  383,  a)  consists  of  a  dense  plexi- 
form  arrangement  of  the  axones  of  the  above- described  olfactory  cells. 
From  this  layer  the  axones  pass  into  the  layer  of  olfactory  glomeruli 
where  their  terminal  ramifications  mingle  with  the  dendritic  terminals 
of  cells  lying  in  the  more  dorsal  layers,  to  form  distinctly  outlined 
spheroidal  or  oval  nerve-fibre  nests,  the  olfactory  glomeruli  (Fig.  383, 
og) .  The  latter  mark  the  ending  of  neurone  system  No.  I.  of  the  olfac- 
tory conduction  path.     (For  olfactory  tract  see  pp.  475,  477,  a.) 

The  molecular  layer  contains  both  small  nerve  cells  and  large 
nerve  cells.  These  send  their  dendrites  into  the  olfactory  glomeruli. 
The  smaller  cells  belong  to  Golgi  Type  II.  (seepage  132)  and  appear 
to  be  association  neurones  between  adjacent  glomeruli.  The  axones 
of  the  larger  cells,  the  so-called  brush  cells,  become  fibres  of  the  olfac- 
tory tract. 

Of  the  mitral  cells  (Fig.  383,  me),  the  main  dendrites  end  in  the 
olfactory  glomeruli,  while  their  axones,  Hke  those  of  the  brush  cells, 
become  fibres  of  the  olfactory  tract. 

In  addition  to  the  fibres  which  pass  through  it  (axones  of  mitral 
and  of  brush  cells),  the  granular  layer  contains  numerous  nerve  cells. 
Many  of  these  are  small  and  apparently  have  no  axones  (amacrine 
cells).  Their  longer  dendrites  pass  toward  the  periphery,  their 
shorter  dendrites  toward  the  olfactory  tract.  Larger  multipolar  cells, 
whose  axones  end  in  the  molecular  layer,  also  occur  in  the  granular 
layer. 

The  layer  of  longitudinal  fibre  bundles  consists  mainly  of  the 
centrally  directed  axones  of  the  mitral  and  brush  cells.  These  fibres 
run  in  distinct  bundles  separated  by  neuroglia.  Leaving  the  bulb 
they  form  the  olfactory  tract  by  means  of  which  they  pass  to  their 
cerebral  terminations. 

The  brush  cells  and  mitral  cells  with  their  processes  thus  consti- 
tute neurone  system  No.  II.  of  the  olfactory  conduction  path. 

TECHNIC 

(i)  Carefully  remove  the  olfactory  portion  of  the  nasal  mucosa  (if  human 
material  is  not  available,  material  from  a  rabbit  is  quite  satisfactory).  This  may 
be  recognized  by  its  distinctly  brown  color.  Fix  in  Flemming's  fluid  (technic  7, 
p.  7),  or  in  Zenker's  (technic  9,  p.  8).  Stain  thin  vertical  sections  with  haemat- 
oxylin-eosin  (technic  i,  p.  20)  and  mount  in  balsam. 

(2)  For  the  study  of  the  nerve  relations  of  the  olfactory  cells  material  should 
be  treated  by  the  rapid  Golgi  method  (page  35). 


THE  ORGANS  OF  SPECL\L  SENSE 


587 


The  Organ  of  Taste 

The  organ  of  taste  consists  cf  the  so-called  taste  buds  of  the  Ungual 
mucosa.  These  have  been  mentioned  in  connection  with  the  papilloe 
of  the  tongue  (page  226)  and  under  sensory  end-organs  (Fig.  297). 

The  taste  buds  are  found  in  the  side  walls  of  the  circumvallate 
papillae  (page  226),  of  some  few  of  the  fungiform  papillae,  in  the 
mucosa  of  the  posterior  surface  of  the  epiglottis,  and  especially  in 
folds  (foliate  papilla?)  which  occur  along  the  postero-lateral  margin 
of  the  tongue. 

The  taste  bud  (Fig.  384)  is  an  ovoid  epithehal  structure  embedded 
in  the  epithelium  and  connected  with  the  surface  by  means  of  a  min- 
ute   canal,    the   gustatory   canal    (Fig.  ^ 
384,  a),   the  outer  and  inner   ends   of 
which  are  known,  respectively,  as  the 
outer  and  inner  taste  pores. 

Each  taste  bud  consists  of  two 
kinds  of  cells,  neuro-epithelial  cells  or 
gustatory  cells  and  sustentacular  cells 
(Fig.  384).  The  gustatory  cells  are 
long,  delicate,  spindle-shaped  cells 
which  occupy  the  centre  of  the  taste 
bud,  each  ending  externally  in  a  cilium- 
like  process,  which  usually  projects 
through  the  inner  pore.  The  inner  end 
of  the  cell  tapers  down  to  a  fine  process, 
which  may  be  single  or  branched.  The 
sustentacular  cells  are  long,  slender 
cells  which  form  a  shell  several  cells  thick  around  the  gustatory 
cells.  Sensory  terminals  of  the  glosso-pharyngeal  nerves  (Fig. 
384,  h)  end  within  the  taste  buds  in  a  network  of  varicose  fibres — 
inlrageminal  fibres.  Other  sensory  terminals  of  the  same  nerve  end 
freely  in  the  epithelium  between  the  taste  buds.  These  are  finer 
and  smoother  than  the  intrageminal  fibres  and  are  known  as  inter- 
geminal  fibres  (Fig.  384). 


Fig.  384. — Taste-bud  from 
Side  Wall  of  Circumvallate  Pa- 
pilla. (Merkel-Henle.)  (/,  Taste- 
pore;  b,  nerve  fibres,  some  of 
which  enter  the  taste-bud — in- 
trageminal fibres;  while  others 
end  freely  in  the  surrounding 
ei)ithelium — intcrgcminal  fibres. 


TECHNIC 

(i)  The  general  structure  of  the  taste  buds  is  shown  in  the  sections  of  tongue 
(technic,  p.  227). 

(2)  For  the  study  of  the  nerve  terminals  the  method  of  Golgi  should  be  used 

^Pagc.35)- 


588  THE  ORGANS 

General  References  for  Fuither  Study 

KoUiker:  Handbuch  der  Gewebelehre  des  Menschen. 
McMurrich:  The  Development  of  the  Human  Body. 
Ramon  y  Cajal:  La  retine  des  vertebres.     La  Cellule,  ix.,  1893. 
Schwalbe:  Lehrbuch  der  Anatomic  der  Sinnesorgane.  1887. 


INDEX 


Abducens  (nerve  VI),  475,  499,  502 
Absorption,  273 

of  fat,  273 
Accessorius  (nerve  XI;,  4S3 
Accessory  nasal  sinuses,  299 

olivary  nucleus,  490 
Achromatic  element  of  intranuclear  net- 
work, 48 

spindle,  54 
Acid  aniline  dyes,  20 

cells,  245,  249,  272 
Acidophile  granules,  ic6 
Acini,  217 
Acoustic    group    of  segmental    neiu-ones, 

475 
Acromegaly,  409 
Acrosome,  343 

Acusticus  (nerve  VIII),  475,  481,  491,  493 
Adelomorphous  cells,  249 
Adenoids,  i8o 
Adipose  tissue,  87 
Adrenal  gland,  412 

blood-vessels  of,  414 

chromaflin  granules  of,  414 

development  of,  415 

lipoid  granules  of,  412 

lymphatics  of,  414 

nerves  of,  414 

pha;ochrome  granules,  414 

phaK)chromoblasts,  415 

sympathoblasts,  415 
Adventitia  of  arteries,  156 

of  lymph  vessels,  165 

of  veins,  158 
Afferent  cerebellar  neurones,  490,  493,  501, 

504,  507 
peripheral  nerves,  419 

segmental  neurones,  47C 
paths,  47^) 

pallia!,  461,  462,  464,  474,  476,  523 
roots,  their  terminal  nuclei  and  sec- 
ondary tracts,  483,485,489,491, 
500,  504,  506,  515,  520,  524,  526, 

suprascgmental  neurones,  421 


Agminated  follicles,  260 
Air  cells,  310 

passages,  310 

sacs,  310 

vesicles,  310 
Ala  cinerea,  481,  489 
Alcohol,  as  a  fixative,  6 

dilute,  as  a  fixative,  6 

for  hardening,  8 

Ranvier's,  4 

strong,  as  a  fixative,  6 
Alcohol-ether  celloidin,  1 1 
Alimentary  tract,  219 

development  of,  296 

endgut,  263 

foregut,  243 

headgut,  220 

midgut,  255 
Altmann's  granule  theory  of  protoplasmic 

structure,  44 
Alum-carmine,  19 

for  staining  in  bulk,  21 
Alveolar  ducts,  310 

glands,  215,  217 

passages,  311 

sacs,  310 
Alveoli,  217,  282,  309 
Amacrine  cells,  558,  596 
Amitosis,  53 
Amoeboid  movement,  5 1 

technic  for,  63 
Amphiaster,  54 
Amphicytes,  427 
Amphipyrenin,  48 
Ampulla,  574 

Amygdaliform  nucleus,  536 
Anabolism,  50 
Anaphase,  56 
Aniline  dyes,  acid,  20 

basic,  19 
Anistropic  line,  115 

substance,  1 15 
Annular  terminations,  434 
Annuli  fjbrosi,  162 
Ansa  ienticularis,  536 


589 


590 


INDEX 


Anterior   corpus   quadrigemini,    517, 
522 

cerebral  commissiire,  532,  536 

horns,  444,  448 

root  or  motor  cells  of,  441,  444 

perforated  space,  532,  536 

pyramids,  464 

white  commissure,  536 
Antero-lateral  funiculus,  448 

white  column,  448 
Antrum,  355 
Anus,  267 
Aorta,  156 

Apathy,  concerning  cilia,  76 
Apical  body,  343 
Aponeurosis,  92 
Appendix  epididymidis,  342 

testis,  342 

vermiformis,  265 
Aqueductus  Sylvii,  417,  515,  517 
Arachnoid  membrane,  422,  560 
Arbor  vit<E,  507 
Arborescent  terminations,   434 
Arborizations,  terminal,  131,  429 
Arc,  cerebellar,  470 

cerebral,  470 

palhal,  471 

spinal  reflex,  469 

three-neurone,  469,  506 

two-neurone,  469,  504 
ArchipaUium,  532 
Archoplasm,  49 
Arciform  nucleus,  499,  530 
Arcuate  fasciculus,  535 

fibres,  487,  491,  499 
external,  487,  490,  499 
internal,  487,  500,  502,  522 
Area,  acustica,  482 

hippocampal,  539 

tegmenti,  530 
Areolar  (loose)  connective  tissue,  87 
Arrector  pili  muscle,  391 
Arrectores  pilorum,  394 
Arteriae  arciform es,  326 

rectffi,  328 
Arteries,  153 

adventitia  of,  156 

anterior  spinal,  454 

aorta  and  other  large,  156 

arcuate,  326 

arteriole,  154 

bronchial,  313 


Arteries,  carotid,  411 
ciHary,  565 
coats  of,  153 
coronary,  161 
development  of,  163 
greater  arterial  circle  of  iris,  566 
hepatic,  289 
interlobar,  326 
interlobular,  326 
intima  of,  154 
large,  like  the  aorta,  156 
lesser  arterial  circle  of  the  iris,  566 
lymph  channels  of,  159 
media  of,  155 
medium-sized,  154 
nerves  of,  159 
phrenic,  328 
posterior  spinal,  454 
precapillary,  154 
pulmonary,  313 
recurrent,-328 
renal,  318,  325 
small,  153 

structural  peculiarities  of  some,  157 
sulco-commissural,  454 
technic  of,  160 
vasa  vasorum,  159 
Arteriole,  154 
Articular  cartilages,  204 
Articulations,  204;  see  Joints 
diarthrosis,  204 
synarthrosis,  204 
synchondrosis,  204 
syndesmosis,  204 
technic  of,  205 
Arytenoid  cartilages,  301 
Ascending  degeneration,  459 

fibre  tracts  of  spinal  cord,  445,  459 

direct  cerebellar,  463 

Gowers',  464 

long  arms  of  dorsal  root  fibres,  461 

posterior  columns,  443,  448 
funiculi,  448,  461 

spino-tectal,  465 
-thalamic,  462 
tract  of  Flechsig,  463 
tracts  forming  parts  of  afferent  pal- 
lial  paths,  461 

to  cerebellum,  463 
tractus  spino-cerebeUaris  dorsalis,  463 

ventralis,  463 
uncrossed  cerebellar,  463 


INDEX 


591 


Asters,  58 

Atresia  of  follicle,  363 

Atrophj-    method    of    determining    fibre 

tracts  of  the  cord,  459 
Attraction  sphere,  49 
Auditory  canal,  572 

cells,  581 

hairs,  575 

nerve.  491,  493 

cochlear  branch  of,  491,  493 
vestibular  branch  of,  475,  491,  493 

path,  475,  491,  492,  493,  524 

pit,  583 
Auerbach,  end-buttons  of,  38 

end-feet  of,  38 

plexus  of,  264,  270 
Auricle,  573 

muscle  of,  161 
Auriculo-ventricular  ring,  161 
Axis  cjlinder,  126,  132;  see  also  Axone 
.Axolemma,  134 

and  neurilemma,  relation  of,  136 
Axonal  degeneration,  142,  459 
Axone,  the,  126,  132,  418 

Bethe's  views  of,  136 

Cajal's  views  of,  137 

collaterals  of,  132 

degenerative  changes  in,  139 

development  of,  418 

fibres  of  Remak,  133 

medullary  sheath  of,  132 

meduUated,  133 

naked  axone,  132 

non-medullated,  132 

terminal  arborizations  of,  132 
Axone-hill,  132 

Baillargkr,  Hne  of,  541 
Balsam,  Canada,  for  mounting,  23 
Barker,  concerning  the  neurone,  127,  130 
Bartholin,  glands  of,  376 

duct  of,  277 
Basal  filament,  213 

granule,  76 
Basic  aniline  dyes,  19 
Basket  cells,  222,  510 
Basophile  granules,  106 
Bellini,  duct  of,  321,  324 
Berkley,  concerning  pituitary  body,  409 
Bertini,  columns  of,  320 
Bethe,     ccncerning    continuity    of    axo- 
lemma  and  neurilemma,  136 


Betz,  cells  of,  533,  536,  539 
Bioblasts,  44 

Bipolar  nerve  cells,  127,  428 
Bladder,  urinary,  330 
Blastoderm,  62 
Blastomeres,  62 
Blocking,  12 
Blood,  103 

corpuscles,  103 

crenation  of  red  cells,  104 

development  of,  108 

diapedesis,  107 

dust,  ic8 

erythrocytes  of,  103 

granules,  elementary,  ic8 

granules  of  EhrUch,  107 

hajmatin,  104 

hsmatokonia,  108 

haemoglobin  of,  104 

haemolysis,  104 

Jenner's  stain  for,  31 

leucocytes  of,  105 

macrocytes,  103 

microcytes,  103 

phagocytosis,  107 

plasma  of,  103 

platelets,  108 

red  cells  of,  103 
crenation  of,  104 
technic  for,  63 

smears,  technic  of,  no 

specific  gravity  of,  103 

stroma  of,  104 

technic  of,  no 

thrombocytes,  108 

vascular  unit,  313 

white  cells  of,  105 
Blood-islands,  io8,  163 
Blood-sinuses  of  haimolyniph  nodes,  173 
Blood  smear,  6 
Blood-vascular  unit,  313 
Blood-vessel  system,  151 

arteries,  153 

capillaries,  151 

development  cf,  163 

heart,  161 

lining  of,  151 

technic  of,  160,  163 

vasa  vasorum,  159 

veins,  158 
Blood-vessels,  151 

lymph  channels  of,  159 


592 


INDEX 


Blood-vessels,  nerves  of,  159 

technic  of,  160 
Body  cavities,  144 
Bone,  breakers,  199 
cells,  190,  200 
decalcification  of,  10 
formers,  198 
tissue,  100 

calcination  of,  loi 

cells  of,  loi 

cementum,  233 

corpuscles  of,  loi 

decalcification  of,  3,  9,  loi 

intercellular  substance  of,  loi 

lacunae  and  canaliculi  of,  loi 

lamellae  of,  loi 

technic  of,  102 
Bone-marrow,  192 

blood-vessels  of,  196 
development  of,  203 
gelatinous,  195 

marrow  spaces,  188,  189,  198,  200 
red,  194 

cells  of,  190 

erythroblasts  of,  192 

fat  cells  of,  193 

giant  cells,  193 

leucocytes,  193 

marrow  cells,  192 

mast  cells  of,  193 

megakaryocytes,  193 

myelocytes  of,  192 

myeloplaxes  of,  193 

non-nucleated  red  blood  cells  of, 

193 

normoblasts,  192 

nucleated  red  blood  cells  of,  192 

osteoclasts.  193 

plasma  cells  of,  193 

polykaryocytes  of,  193 
technic  of,  197 
yellow,  195 
Bones,  188 

blood-vessels  of,  195 
canaliculi  of,  191 
cancellous  or  spongj-,  188 
cells  of,  190,  200 

origin  of,  19S 
circumferential  lamellae  of,  191 
development  of,  197 

intracartilaginous,  199 

intramembranous,  197 


Bones,   subperichondral   development  of, 
201 
subperiosteal,  201 
growth  of,  203 
hard  or  compact,  188 
Haversian  canals  of,  189 
lamellae,  190 
spaces,  202 
Howship's  lacunae,  199 
intermediate  lamellae,  191 
interstitial  lamellae,  191 
lymphatics  of,  196 
marrow,  192 
red,  194 
yellow,  195 
nerves  of,  196 
nutrient  canal,  196 
foramen,  196 
vessels,  196 
osteoblasts,  198 
osteoclasts,  199 
osteogenetic  tissue,  197 
perforating  fibres,  192 
perichondrium,  199 
pericranium,  198 
periosteal  buds,  200 
periosteum  of,  191,  199 
Sharpey's  fibres,  192 
technic  of,  196 

developing  bone,  203 
Volkmann's  canals,  191,  196 
Bony  cochlea,  576 

spiral  lamina,  577 
Borax-carmine,  alcoholic  solution,  22 
Born's  theory  of  corpus  luteum,  362 
Bowman,  capsule  of,  320,  322 
glands  of,  300 
membrane  of,  548 
sarcous  elements  of,  116 
Brachia  conjunctiva,  502,  517 
Brachium  of  posterior  corpus  quadrigem- 
inum,  520 
pontis,  499 
Brain,  the,  473 

cerebral  cortex  of,  536 
contrasted  with  spinal  cord,  473 
development  of,  416 
efifectors,  473 

endbrain  (telencephalon) ,  417,  532 
corpus  striatum,  532 
palhum,  533 
rhinencephalon,  532 


INDEX 


593 


Brain,  forebrain  {prosencephalon) ,  416,  522 
diencephalon      {thalamencephalon) , 
417,  522 
epithalamus,  523 
h}-pothalamus,  523 
thalamus,  523 
interbrain,  522 
general  histology  of,  479 

structure  of,  473 
hemispheres  of,  478 
higher  coordinating  apparatus  of,  473 
hindbrain     (rhombencephalon),     417, 

479 

cerebellum,  499 

isthmus,  515 

medulla  oblongata  (bulb),  479 

nerves  of,  479 

pons,  417,  482,  499 

tegmentum,  479,  499 
membranes  of,  422 

arachnoid,  422 

blood-vessels  of,  422 

cerebral  dura,  422 

diura  mater,  422 

pia  mater,  422 
cerebrahs,  424 

Pacchionian  bodies  of,  424 

relation  of  optic  nerve  to,  560 

technic  of,  424 
midbrain  (mesencephalon),  416 

aqueductus  Sylvii,  517 

basis  peduncuU,  517 

corpora  quadrigemina,  478,  522 

iter,  517 

pes  pedunculi,  521 

posterior  commissure,  522 

substantia  nigra,  521 

tegmentum,  517 
pallium,  478 
pineal  eye,  544 
pituitary  body,  407 
receptors,  473 

relation  of,  to  optic  nerve,  560 
sand,  547 
segmental  brain  and  nerves,  420,  474 

afferent  peripheral  neurones,  474 

efferent  peripheral  neurones,  475 
semicircular  canals,  473 
suprasegmental  structures,  478 
technic  of,  482,  543 
ventricles,  416,  417 
vesicles,  416 

38 


Branca,  concerning  the  centrosome,  58 
Bridges,  intercellular,  3,  70,  112 
Bronchi,  304 

alveolar,  309 

blood-vessels  of,  313 

cartilages  of,  306 

development  of,  315 

lobular,  309 

lymphatics,  315 

nerves  of,  315 

primary,  304 

respiratory,  310 

structure  of  walls  of,  304 

technic  of,  317 

terminal,  310 
Bruch,  membrane  of,  551 
Brunner's  glands,  252,  262,  272 
Bulb,  479;  see  Medulla 
Bulbus  ocuh,  548;  see  Eyeball 
Bundle  of  Lowenthal,  466 

of  Vicq  d'Azyr,  524,  532 
Burdach,  column  of,  459,  462 

nucleus  of,  482,  481 
Bursae,  208 

Busch-Marchi  staining  method,  35 
Biitschli's    theory    of   protoplasm    struc- 
ture, 44 

diagram  of,  45 

Cachexia  strumipriva,  403 
Cajal,  cells  of,  536 

concerning    the    neurone,    131,    135, 
138 

interstitial  nucleus  of,  465,  485,  491, 
SCO,  504 

methods  for  staining  neurofibrils  in 
nerve  cells,  37 
Cajeput  oil  for  clearing  sections,  23 
Calcarine  area,  543 
Calcification,  82 

centre,  197,  200 

zone,  202 
Calcination,  539 
Canada  balsam,  23 
Canal,  gastro-inlcslinal,  245 

gustatory,  587 

lacrymal,  567 

of  Cloquet,  565 

of  Petit,  565 

of  Schlcmm,  554 

I)ortal,  290 

Volkmann's,  191,  196 


594 


INDEX 


Canaliculi  of  bone,  loi,  191 

of  connective  tissue,  83 
Canalis  communis,  575 
Canalized  fibrin,  373 
Cancellous  bone,  188,  198 
Capillaries,  151 

chyle,  270 

development  of,  163 

technic  of,  160 
Capillary  endothelium,  151 

network,  152 
Capsule  of  Bowman,  320,  322 

internal,  530 

of  gangUon  cells,  419 

of  Glisson,  287 

of  Tenon,  566 
Carbol-xylol  for  clearing  specimens,  23 
Carboxyhaemoglobin,  107 
Carmine  alum,  19,  21 

borax,  22 

gelatin,  25 

neutral,  20 

picro-,  21 
Carotid  gland,  409 
Cartilage,  97 

arytenoid,  301 

cells,  98 

chondrin,  98 

classification  of,  98 

cricoid,  301 

development  of,  81,  100 

elastic,  99 

embryonal,  99 

epiphyseal,  203 

fibrous,  99 

hyaline,  98 

intercellular  matrix  of,  100 

intermediate,  199 

laryngeal,  540 

of  developing  bone,  199 

perichondrium  of,  99 

Santorini's,  301 

technic  of,  100 

thyreoid,  301 

tracheal,  302 

Wrisburg's,  301 
Cartilages,  articular,  204 

costal,  204 

skeletal,  204 
Caryochromes,  129,  512 
Caudate  nucleus,  526,  532,  535 
Cavernous  sinuses,  350 


Cavity  of  embryonic  vesicle,  61 
Cedarwood  oil  as  solvent,  13 
Cell,  the,  43 

amitosis,  53 
body  of,  44,  126 
centrosome  of,  49 
crusta  of,  46 
cuticula  of,  47 
cytoplasm  of,  45 
cytoreticulum  of,  45 
deutoplasm  granules  of,  46 
division,  direct,  53 

indirect,  53 
endoplasm  of,  46 
exoplasm  of,  46 
function  of,  51 
hyaloplasm  of,  44 
intranuclear  network  of,  48 
irritabihty  of,  51 
karyoplasm  of,  46 
linin  of,  48 
membrane  of,  47 
metabolism  of,  50,  213 
metaplasm  granules  of,  46 
microsomes,  44 
mitosis,  53 
motion  of,  5 1 
nuclear  membrane  of,  48 
nuclein  of,  48 
nucleolus  of,  48 
nucleoreticulum,  48 
nucleus,  47 
origin  of  word,  47 
patches,  373 

paraplasm  granules  of,  46 
plastids,  46 
plastin,  44 
protoplasm  of,  43 

Altmann's  granule  theory  of,  44 

Biitschli's  foam  or  emulsion  theory 
of,  44 

fibrillar  theory  of,  45 
reproduction  of,  52 
space  (lacuna),  loi 
spongioplasm  of,  44 
technic  for  study  of,  44 
trophospongium,  46 
typical,  43 

diagram  of,  43 

structure  of,  43 
vital  properties  of,  50,  213 
function  of,  285 


INDEX 


595 


Cell,  function  of,  Opie's  theory  of,  286 
origin  of,  285 
structure  of,  285 
technic  of,  287 
Cell-islands  of  Langerhans,  285 
Celloidin,  alcohol-ether,  11 

clove-oil,  12 

embedding,  11 

sections,  14 
clearing  of,  23 
mounting  of,  2^ 
Cells,  acid,  245,  249,  272 

active,  212 

adelomorphous,  249 

air,  310 

amacrine,  558,  586 

amoeboid,  144 

auditor}',  581 

basal,  300 

basket,  222 

blood,  103 

bone,  loi,  190,  200,  233 

brush,  585 

capsule,  418 

cartilage,  98,  201 

cementoblasts,  235 

central,  249 

centro-acini,  of  Langerhans,  283 

centro-tubular,  283 

chief,  245,  249,  272,  405,  407 

chromafEn,  410 

chromophile,  407 

ciliated,  75,  304 

clasmocytes,  85 

clasmatocytes,  85 

clear,  405 

colloid,  403,  405 

compound  tactile,  43 1 

connective-tissue,  83 

corneum,  383 

crescents  of  Glanuzzi,  222,  278,  302 

daughter,  57 

decidual,  370 

Deiter's,  580 

delomorphous,  249 

demilunes  of  Heidcnhain,  222 

empty,  212 

endothelial,  151 

eosinophile,  106,  174 

qjithelial,  70 

erythroblasts,  192 

erythrocytes,  103 


Cells,  extrinsic,  443 
fat,  87,193 
fibroblasts,  82 
fixed,  83 
foetal,  312,  316 
gangha,  419 
giant,  193 
gland,  212 

goblet,  75,  212,  257,  272 
Golgi,  Type  I.,  130,  132 

Type  II.,  132,  446 
granule,  538 
gustatory,  587 
hair,  575,  581 
hecatomeric,  445 
Hensen's,  580 
heteromeric,  445 
interstitial,  33'*^ 
intrinsic,  443 
KupfTer's,  292 
Langerhans',  283 
leucocytes,  103,  193 
Leydig's,  568 
liver,  290 
loaded,  212 
lutein,  359 
lymphoid,  170 
macrocytes,  103 
marrow,  192 
mast,  83,  174,  192 
megakaryocyte,  193 
megalocyte,  184 
microcyte,  103 
migratory  leucocytes,  259 
mitral,  586 
mononuclear,  184 
mossy,  143 

mucous,  212,  221,  257,  272 
multinuclear,  184 
muscle.  III 
myelocytes,  192 
mycloplaxcs,  193 
nerve,  11 1;  for    classification    sec 

Nerve  cells 
neurilemma,  144,  419 
ncurobhists,  126,  142,  418 
neuro-e[)ithelial,  575 
neurogha,  143,  418,  453,  514 
normoblasts,  192 
nucleated  red  blood,  108,  192 
0(iont;>l)lasts,  228,  241 
of  ("laudius,  581 


596 


INDEX 


Cells  of  oral  glands,  221,  222 

olfactory,  300 

osteoblasts,  198,  235 

osteoclasts,  193,  199,  235 

ovum,  52,  3SS,  356 

oxyntic,  249 

oxyphile,  405 

Paneth's,  260,  273 

parietal,  249 

peptic,  249,  272 

phseochromoblasts,  412,  415 

phagocytes,  107,  174 

pigmented,  46,  76,  131,  384,  388,  554 

pillar,  580 

plasma,  85,  193 

polykaryocytes,  193 

prickle,  383,  387 

primitive  ova,  354,  378 

Purkinje,  509 

red  blood,  103,  184 

replacing,  73,  252,  259 

reserve,  403 

respiratory,  311 

resting,  54,  212,  403 

secreting,  213 

serous,  221 

Sertoli's,  335,  378 

sex,  378 

signet-ring,  88 

simple  tactile,  431 

single  primitive,  5  2 

smooth  muscle,  112,  381 

spermatids,  337,  344 

spermatoblasts,  345 

spermatocytes,  337,  344 

spermatogenic,  335 

spermatogones,  336,  344 

spider,  143 

spleen,  184 

supporting,  335 

sustentacular,  284,  300,  335,  575 

sympathoblasts,  415 

tactile,  433 

tautomeric,  445    . 

tendon,  92 

thrombocytes,  108 

wandering,  86,  259 

white  blood,  105,  184 
Cementing  glycerin  mounts,  22 
Cementoblasts,  235 
Cementum,  233 

development  of,  242 


Central  canal,  416,  449 

cells,  249 

chromatolysis,  142 

gelatinous  substance,  449 

gray,  483,  485,  487,  502 

nervous  system,  416 

neurones,  418 

spindle,  54 

tegmental  tract,  490,  501,  507,  515, 
518,  526 

vein,  289 
Centriole,  49 

Centro-acinar  cells  of  Langerhans,  283 
Centrosome,  49,  62 

archoplasm,  49 

attraction  sphere,  49 

centriole,  49 

daughter,  53 

of  fertihzation,  62 
Centro-tubular  cells  of  Langerhans,  283 
Cerebellar  arc,  470 

connections,  463,  464,  468,  499,  506 

cortex,  507,  512 

peduncles,  502 
Cerebello-olivary  fibres,  490,  491,  499 
Cerebellum,  417,  502,  507 

arbor  vitae,  507 

ascending  paths  to  the,  462 

association  cells  of,  514 

basket  ceUs  of,  510 

cells  of,  509,  510,  511 

climbing  fibres  of,  510 

cortex  of,  509,  514 

dentate  nucleus  of,  500,  502,  507 

descending  tracts  from,  464 

development  of,  417 

fibres  of,  510 

climbing,  510,  513 
mossy,  513 
of  Bergmann,  514 
parallel,  512 

general  histology,  507 

glomeruli  of  (islands),  512 

granular  layer,  507 

gray  matter  of,  507 

hemispheres,  of,  502,  507 

internal  nuclei  of,  502,  507 

laminse  of,  507 

middle  peduncle  of,  508 

molecular  layer,  509 

neuroglia  of,  514 

nuclear  layer,  509 


INDEX 


597 


Cerebellum,  nucleus  dentatus,  507 
emboliformis,  507 
globosus,  502,  507 
tecti  or  fastigii,  502,  507,  538 

peduncles  of,  508 

Purkinje  cells  of,  509 

technic  of,  543 

vermis,  507 
Cerebral  arc,  471 

cortex,  481 

dura,  422 

hemispheres,  417 
development  of,  417 

membranes,  422 

peduncles,  518 

vesicle,  416 
Cerebro-spinal  ganglia,  126,  418,  426 
central  processes  of,  436 
Dogiel's  classification  of,  427 
peripheral  processes  of,  429 
technic  of,  441 

nervous  system,  417 

neurones,  efferent  peripheral,  441 
Ceruminous  glands,  572 
Cervical  enlargement  of  cord,  443 

segments  of  cord,  443 
Cervbc,  367 

epithehum  of,  368 

external  os,  368 

ovula  Nabothi,  368 

plicae  palmatae,  368 

technic  of,  379 
Chain  ganglia,  436 
Cheeks,  mucous  membrane  of,  220 
Chemotaxis,  51 
Chiasma,  optic,  526,  561 
Chief  cells,  245,  249,  272,  405,  407 
Chloride  of  gold  for  staining  connective- 
tissue  cells,  28 
Chloroform  as  solvent,  13 
Choledochus  ductus,  295 
Choriocapillaris,  551 
Chorion,  371 
Chorionic  villi,  371 
Chorioid,  the,  550 

choriocapillaris  of,  551 

fissure,  570 

Ilallcr's  layer  of,  551 

lamina  citrea,  551 
suprachorioidca,  551 

perichorioidal  lymph  spaces  of,  551 

plexus,  417,482,487,  502 


Chorioid,  tapetum  cellulosum  of,  551 
fibrosum  of,  551 
ven£e  vorticosas  of,  551 
vitreous  membrane  of,  552 
ChromafEn  cells,  410 
granules,  412 
organs,  410 

Rose,  concerning     chromaffin     cells, 
410 
Chromatic   element   of   intranuclear  net- 
work, 48 
Chromatin,  48 
Chromatolysis,  142 
Chromatolytic  changes,  363 
Chrome-silver  method  of  Golgi,  29 
Chromophihc  bodies,  129 

significance  of,  130,  138 
Chromosomes,  55 
daughter,  55 
Chyle  vessels,  270 
Cilia,  52,  71,  76,  340 
Ciliary  artery,  565 
body,  552 

blood-vessels  of,  565 
canal  of  Schlemm,  554 
hgamentum  pectinatum,  554 
muscles  of,  552 
processes  of,  552 
spaces  of  Fontana,  554 
vitreous  membrane  of,  553 
ganglion,  436 
movement,  52 

technic  for,  570 
muscle,  553 
plexus,  566 
processes,  552 
Cingulum,  535 
Circulatory  system,  151 

blood- vessel  system,  151 
carotid  gland,  410 
coccygeal  gland,  411 
development  of,  163 
lymph-vessel  system,  166 
Circumferential  lamclL-c,  191 
Circumvallatc  i)apillx,  225 
Cirl,  concerning  fibres  of  internal  capsule, 

526 
Clarke's  columns,  450,  455,  463 
Clasmatocytes,  85 
Clasmocytes,  85 

Claude,  concerning  development  of  pan- 
creas, 297 


598 


INDEX 


Claudius,  cells  of,  581 

Clava,  the,  481 

Clearing  specimens  before  mounting,  23 

Clefts  of  Schmidt-Lantermann,  135 

Climbing  fibres,  510,  513 

Clitoris,  376 

Cloquet's  canal,  565 

Closed  skein  (spireme),  54 

Clove -oil  celloidin,  12 

Coagulum  sheath,  137 

Coccygeal  glands,  411 

segments  of  spinal  cord,  455,  488 
Cochlea,  576 

bony  spiral  lamina  of,  577 

cupola  of,  576 

cupula  of,  576 

hamulus  cf,  577 

helicotrema,  578 

membranous  spiral  ligament  of,  577 

modiolus  of,  576 

scala  tympani,  578 

vestibuli,  578 
spiral  ligament  of,  577 
Cochlear  duct,  578 

basilar  membrane  of,  579 
crista  basilaris,  579 
external  spiral  sulcus,  579 
membrane  of  Reissner,  579 
organ  of  Corti,  580 
spiral  prominence  of,  579 
stria  vascularis,  579 
zona  pectinata,  580 
tecta,  580 
nerve,  475,  489,  491,  493 
tracts,  491,  500,  504 
Coelom,  165 
Cohnheim's  field,  116 
Collagenous  fibres,  81 
Collaterals,  132,  447 
Colliculi,  417,  517,  522 
Colloid,  402,  405,  408 
Colostrum  corpuscles,  400 
Column  cells,  444 

hecateromeric,  444 
heteromeric,  444 
tautomeric,  444 
technic  of,  445 
of  Burdach,  459,  462,  481,  487 
of  Goll,  459,  462,  481,  487 
Columnse  rectales.  266 
Columns  of  Bertini,  320 
of  Sertoli,  335 


Comma  tract  of  Schultze,  467 
Commercial  form.aUn,  4 
Commissura  habenularis,  531 
Commissural  fibres,  532 
Common  dental  geim,  238 

senses,  436 
Compact  bone,  188 
Compound  tactile  cells,  431 
Conduction  path,  421,  461 

afferent  pallial,  461,  476 

afferent  and  efferent  suprasegmental, 
476 

auditory,  493 

descending  suprasegmental,  483 

efferent  cerebellar,  499 
pallial,  476 

pallio-cerebellar,  499 

pallio-spino-peripheral  efferent,  465 

to  cerebellum,  462 

trigeminal  afferent  pallial,  507 
Cone  association- neurones,  561 

fibres,  557 

neurones,  560 

-visual  cell,  557 
Cones,  layer  of  rods  and,  556 
Conjunctiva,  568 

end  bulbs  of,  433,  569 
Connective  tissue,  80,  82 

adipose  or  fat,  87 

aponeurotic,  92 

areolar,  87 

bone,  IDG 

cartilage,  97 

cells  of,  83 

characteristics  of,  80 

chlorid-of-gold   method   for    demon- 
strating cells  of,  28 

classification  of,  81 

dense  fibrous,  87 

elastic,  92 

elastin  of,  87,  95 

embryonal,  81,  82,  197,  203 

fat,  87 

fibres  of,  86 
elastic,  86 
fibrillated,  86 
reticular,  94 
white,  86 
yellow,  86 

fibrillar,  82 

fibroblasts,  82 

fixed  cells  of,  83 


INDEX 


599 


Connective  tissue,  formed,  91 

gelatin  of,  86 

gelatinous,  82 

histogenesis  of,  80 

intralobular,  91,  215 

interalveolar,  313 

intercellular  substance  of,  86 

interlobar,  215 

interlobular,  89,  215 

intrafascicular,  208,  425 

ligaments,  91 

loose,  87 

Mallory's  stain  for,  29,  30 

mast  cells  of,  83 

mucous,  82 

neuroglia,  142,  418,  453,  514 

pigmented  cells  of,  87 

plasma  cells  of,  83 

reticular,  94 

retinaculcc  cutis,  382 

staining  cells  of,  29 

technic  for,  95,  102 

theories  of  development  of  fibres  of, 
81 

wandering  cells  of,  83 
Constrictions  of  Ranvier,  134 
Contact  theory  of  neurones,  138 
Continuity  theory  of  neurones,  139 
Convoluted  tubules,  320,  322,  323 
Cord,  spinal,  416;  see  Spinal  Cord 
Corium,  380;  see  Derma 
Cornea,  the,  548 

anterior  elastic  membrane  of,  549 
epithelium  of,  549 

corpuscles  of,  550 

endothelium  of  Descemet  of,  550 

membrane  of  Bowman  of,  548 
of  Descemet  of,  550 

posterior  elastic  membrane  of,  550 

substantia  propria  of,  550 
Corneal  corpuscles,  550 
Cornu  ammonis,  532 
Cornua  of  cord,  448 
Corona  radiata  of  ovum,  356 

of  pallium,  533,  536,  537 
Coronary  arteries,  162 
Corpora  amylacea,  348 

cavernosa,  349 

lutea  of  pregnancy,  360 
spuria,  360 
vera,  360 

mammillaria,  531 


Corpora,  quadrigemina,  417,  493,  517 

anterior,  517,  522 

development  of,  417 

posterior,  493,  517 
striata,  417 
Corpus  albicans,  360 
callosum,  536 
dentatum,  502 
haemorrhagicum,  359 
Highmori,    or     mediastinum    testis, 

333 
luteum,  359 

theory  of,  362 
Luysii,  523 

quadrigeminum,  anterior,  517,  522 
spongiosum,  349 
striatum,  532,  535 
caudate  nucleus,  532 
lenticular  nucleus,  532 
putamen,  535 
subthalamicura,  521,  530 
trapezoideum,  500,  504 
Corpuscles,  blood,  103 
bone.  Id 
colostrum,  400 
corneal,  550 
crescentic,  348 
Golgi-Mazzoni,  394,  434 
Grandry's,  431 
Hassall's,  177 
Meissner's,  350,  394,  432 
Merkel's,  431 
Pacinian,  196,  350,  433 
renal,  320 
Ruftini's,  394,  434 
salivary,  i8c 
splenic,  182 
tactile,  432 
Vater-Pacinian,  394 
Wagner,  394 
Cortex  ccrebelli,  509,  514;  see  also   Cere- 
bellum 
cerebri,  533,  536 
areas  of,  541 
association  fibres  of,  543 
barren  or  molecular  layer  of,  538 
cells  of,  536,  539 
of  Betz,  536 
of  Cajal,  537 
of  Gclgi,  Tyjjc  II.,  536 
of  Martinotti,  536,  539 
I)yramidal,  536 


600 


INDEX 


Cortex  cerebri,  commissural  fibres,  533 
corona  radiata  of,  533,  536 
deep  tangential  fibres  of,  541 
external  granular  layer,  539 
ganglionic  layer,  539 
horizontal  cells  of  Cajal,  536 
internal  granular  layer,  539 
interradiary  plexus,  541 
inverted  pyramidal  cells  of  Marti- 

notti,  536 
layer  of  polymorphous  cells,  536 

of  pyramidal  cells  of,  539 
line  of  Baillarger,  541 

of  Gennari,  543 
molecular  layer,  538 
multiform  layer,  539 
plexiform  layer  of  Cajal,  538 
polymorphous  cells  of,  536 
projection  fibres,  543 
radiations  of  Meynert,  541 
stellate  cells  of,  536 
superficial,    tangential     fibres    of, 

541 
supraradiary  plexus  of,  541 
Cortical  labyrinths,  320 

pyramids,  320;  see  also  Kidney 
Corti's  arches,  581 

organ,  580;  see  also  Organ  oj  Corti 

tunnel,  580 
Cotyledons,  371 
Cowper's  glands,  348 
technic  of,  349 
Cox-Golgi  method  of  staining  nerve  tis- 
sue, 36 
Cranial  nerves,  474,    545,    546;    see    also 

Nerves,  cranial 
Crenation  of  red  blood  cells,  104 
Crescentic  corpuscles,  348 
Crescents  of  Gianuzzi,  222,  278,  302 
Cretinism,  403 
Cricoid  cartilage,  301 
Crista  acustica,  576 

basilaris,  579 
Crossed  pyramidal  tracts,  464,  485 
Crura  cerebri,  518 
Crusta  (exoplasm),  46 
Crypt  of  Lieberkiihn,  252,  260 
Cumulus  ovigerus,  356 
Cuneus,  481,  487 
Cupola,  576 
Cupula,  576 
Cutaneous  sensation,  436 


Cuticle,  382;  see  Epidermis 
Cuticula,  47,  71 

dentis,  233 
Cuticular  membrane,  71,  240,  255 
Cystic  duct,  294,  297 
Cytoarchitecture,  541 
Cytoplasm,  46 

of  nerve  cells,  128 
Cytoreticulum,  45 
Cytosomes,  213 

Darksche-witsch,  nucleus  of,  465 
Daughter  cells,  57 

centrosomes,  53 

chromosomes,  55 

stars,  56 
Decalcification,  3,  9 
Decalcifying,  10 

fluids,  10 
Decidua  basalis,  370 

capsularis,  370 

graviditatis,  370 

menstrualis,  369 

placentalls  subchorialias,  374 

reflexa,  370 

serotina,  370 

subchorionic-placental,  374 

vera,  370 
Decidual  cells,  370 

Decolorizing  fluid  for  Weigert's   hema- 
toxylin, 33 
Decussation  of  fillet,  485 

motor,  483 

optic,  561 

of  Forel,  522 

of  Meynert,  522 

of  pyramids,  464,  485,  487 

sensory,  435,  485 
Deep  sensation,  436 
Degenerating    nerves,    Marchi's    method 

for  stairung,  34,  140 
Degeneration  of  neurones,  140 

Wallerian  law  of,  141 
Dehiscent  glands,  217 
Deiter's  cells,  581 

nucleus,  466,  476,  493,  499,  502 
descending  tract  from,  466,   483, 
487,  490,  S02 
Delafield's  hematoxylin,  17 
Delomorphous  cells,  249 
Demilunes  of  Heidenhain,  222 
Dendrites,  the,  126,  131,  418 


INDEX 


601 


Dental  germ,  238 

groove,  238 

papilla,  238 

periosteum,  237 

pulp,  230 

layer  of  Weil  of,  2 28 
odontoblasts,  228 

ridge,  239 

sac,  239 

sheath,  Neumann's,  232 

shelf,  238 
Dentate  nucleus,  458,  500,  502,  507 
Dentinal  canals,  230 

development  of,  241 

fibres  of,  230 

interglobular  spaces  of,  232 

lines  of  Schreger,  232 

nerves  of,  236 

Neumann's  dental  sheath,  232 

Tomes'  granular  layer,  232 
Dentine,  228 

chemical  composition  of,  228 

secondary,  232 
Derma,  or  corium,  380 

corpuscles    of    Meissner,    350,    394, 
432 

muscle  cells  of,  381 

papilla;,  compound,  381 
nerve,  381 
simple,  381 
vascular,  381 

pars  papillaris,  381 
reticularis,  380 

pigmentation  of,  384 

subcutaneous  tissue  of,  381 
Descemet,  endotheUum  of,  550 

membrane  of,  550 
Descending  degeneration,  459 

fibre  tracts  of  the  spinal  cord,  464; 
see  Fibre   tracts   of  spinal   cord 
(descending) 
Deutoplasm,  46,  357 
Diapedesis,  107 
Diaphysis  of  bone,  203 
Diarthrosis,  204 

articular  cartilages,  204 

glenoid  ligaments,  205 

interarticular  cartilages,  205 

joint  capsule,  206 
Diaster,  56,  Go 
Diencephalon,  417,  522 
Digestive  system,  219 


Digestive    system,    alimentary    tract   of, 
219 

development  of,  238,  296 

endgut,  263 

foregut,  243 

gall-bladder,  295 

gastro-intestinal  canal,  245 

headgut,  220 

large  intestine,  263 

larger  glands  of,  275 

liver,  287 

mesentery,  268 

midgut,  255 

mouth,  220 

oesophagus,  243 

omentum,  269 

pancreas,  281 

peritoneum,  267 

pharynx,  242 

rectum,  266 

salivary  glands,  276 

small  intestine,  255 

stomach,  247 

teeth,  227 

tongue,  223 

vermiform  appendbc,  265 
Direct  cerebellar  tract,  463 

pyramidal  tract,  464 
Discus  proligerus,  356 
Dissociation  of  tissue  elements,  4 
Disynaptic  arc,  470 
Dogiel's  end  plates,  350,  567 

theory  of  structure    of    spinal   gan- 
glion, 427 
Dorsal  accessory  olivary  nucleus,  490 

decussation  of  Meynert,  522 

gray  commissure,  449 

root  fibres  of  white  matter,  450 

spino-cerebcllar  tract,  463 

white  commissure,  450 
Duct  systems  of  glands,  214 
Ducts,  aberrans  Halleri,  342 

alveolar,  310 

Bartholini's,  277 

Bellini's,  321,  324 

bile,  290 

cholcdochus,  295 

cochlear,  578 

common,  294 

cystic,  294,  297 

endolymphatic,  575 

ejaculatory,  342 


602 


INDEX 


Ducts,  excretory,  214,  276,  282,  329,  364 

Fallopian  tube,  364 

Gartner's,  363 

hepatic,  289 

mesonephric,  377 

MiiUerian,  348 

nasal,  567 

of  MiiUer  (embryonal),  342 

of  sweat  glands,  384 

oviduct,  364 

pancreatic,  281 

pronephric,  377 

reuniens,  575 

Santorini's,  282 

secondary  pancreatic,  281 

seminal,  339 

Stenoni's,  277 

thoracic,  164 

thyreo-glossal,  403 

utriculo-saccular,  575 

vas  deferens,  340 

epididymis,  339 

vas  efferentia,  339 

Wharton's,  278 

Wirsung's,  281 

Wolffian,  377 
Ductus  aberrans  Halleri,  342 

reuniens,  575 
Duodenum,  262 

Brunner's  glands,  262 
technic  of,  275 
Dura  mater,  422 

blood-vessels  of,  424 

cerebral,  422 

spinal,  422 

technic  of,  424 
Dyes,  acid  aniline,  20 

basic  aniline,  19 

nuclear,  17 

plasma,  19 
Dynamic  centre  of  cell,  57 

Ear,  572;  see  also  Organ  of  Hearing 
blood-vessels  of,  582 
development  of,  583 
drum,  573 
external,  572 

auditory  canal,  572 

auricle,  572 

blood-vessels  of,  573 

ceruminous  glands  of,  572 

ear  drum,  573 


Ear,  external,  auditory  canal,  572 

lymphatics  of,  573 

nerves  of,  573 

pinna,  572 

tympanic  membrane,  573 
internal,  574 

ampuUa,  574 

blood-vessels  of,  581 

canalis  communis,  575 

cochlea,  576 

ducts  of,  578 

ductus  reuniens,  575 

endolymph  of,  574 

endolymphatic  duct,  582 
sac,  582 

fenestra  ovalis,  574 
rotunda,  574 

lymphatics  of,  582 

membrana  tectoria,  582 

membranous  labyrinth,  574 

nerves  of,  582 

organ  of  Corti,  580 

osseous  labyrinth  of,  574 

perilymph  of,  582 

saccule,  575 

scala  media,  578 

semicircular  canals,  575 

utricle,  575 

utriculo-saccular  duct,  575 

vestibule,  574 
middle,  or  tympanum,  573 

fenestra  rotunda  of,  574 

ossicles  of,  574 

stapes,  574 
wax,  573 
Ebner's  glands,  226 

hydrochloric  salt  solution,  10 
Ectoderm,  62 

derivations  from,  67,  126,  142,  395 
Edinger-Westphal  nucleus,  518 
Effectors,  418,  424,  426 
Efferent  pallial  paths,  461,  462,  464,  475, 

477 
peripheral  neurones,  418,   441,   483, 

485,  487,  491,  499,  502,  504,  515, 

518,  524 
root  fibres,  418 
suprasegmental  neurones,   499,   502, 

504,  507,  515,  521,  526,  530,  536 
Egg  cords,  Pfluger's,  354 
technic  of,  366  j 
nests,  354 


INDEX 


603 


Ehrlich,  granules  of,  107 
Ejaculatory  ducts,  341 
Elastic  cartilage,  99 
fibres,  86 
tissue,  92 

Verhoeff's  differential  stain  for,  28 
Weigert's  stain  for,  28 
Elastin,  87,  95 
Eleidin,  383 

Ellipsoid  of  Krause,  557 
Embedding,  11 
celloidin,  11 
parafBn,  13 
Emboliform  nucleus,  507 
Embryonal  tissue,  82 

fat  tissue,  88 
Eminentia  h\T30glossi,  481,  489 

medialis,  481 
Emulsion   theory  of   protoplasmic   struc- 
ture, 44 
Enamel,   233 

cells,  237,  239 

chemical  composition  of,  233 

cuticula  dentis  of,  233 

membrane  of,  240 
development  of,  238 
fibres,  233 
organ,  239 
prisms,  233 

lines  of  Rctzius  of,  233 
Endbrain  (telencephalon),  417,  532 
corpus  striatum,  532 
pallium,  533 

neorjallium,  532 
olfactory  pallium,  532 
rhinencephalon,  532 

anterior  perforated  space,  532 
gyrus  hippocampi,  532 
olfactory  bulb,  532,  595 
nerve,  532 
pyriform  lobe,  532 
trigonum  olfactorium,  532 
tubcrculum  olfactorium,  532 
End-buttons,  509 

of  Aucrbach,  38 
-feet  of  Aucrbach,  38 
-bulbs,  433 

of  Krause,  227,  350,  394 
Endgut,  263 

large  intestine,  263 
mesentery,  267 
omentum,  267 


Endgut,  peritoneum,  267 

rectum,  266 

vermiform  appendix,  265 
Endocardium,  161 

primitive,  164 
Endochondral  ossification,  199 
Endolymph,  574 
Endolj'mphatic  duct,  575 

sac,  575 
Endomysium,  208 
Endoneurium,  133,  425 
Endoplasm,  46 
Endosteum,  195 
Endothelial  tube,  164 
Endothelium,  70 

of  Descemet,  550 
Engelmann,  showing     ciliated    epithelial 

cell,  76 
Entoderm,  62 

tissue  derivations  from,  67,  296,  315 
Eosin,  19 

-glycerin,  22 

-haematoxylin  stain,  20 
Eosinophile  granules,  106,  174     ■ 
Epiblast,  62 
Epicardium,  161 
Epicranium,  198 
Epidermis  (or  cuticle),  382 

eleidin,  383 

keratin,  383 

keratohyaline  granules,  383 

mitosis  of  cells  of,  383 

pareleidin,  384 

pigmentation  of,  384 

prickle  cells  of,  383 

stratum  corneum  of,  383 
oj'lindricum  cf,  383 
germinativum  of,  382 
granulosum  of,  383 
lucidum  of,  383 
Malpighii  of,  382 
mucosum  of,  382 
spinosum  of,  383 
Epididymis,  339 

cells  of,  339 

vas  deferens,  340 

vas  epididymis  of,  3,^0 

vasa  cffcrcntia  of,  339 
Epidural  space,  422 
Eiiiglottis,  301 
Epimysium,  208 
Epineurium,  425 


604 


INDEX 


Epiphyseal  cartilage,  203 
Epiphysis  of  bone,  203 
Epithalamus,  522,  530 
Epithelium,  70 

basal  membrane  of,  70 

ceUs  of,  70 

ciliated,  75 

classification  of,  71 

cuboidal,  72 

cuticular  membrane  of,  71 

endothelium,  77 

follicular,  355 

general  characteristics  of,  70 

germinal,  354,  378 

glandular,  77,  212 

histogenesis  of,  70 

intercellular  bridges  of,  70 

lens,  564 

membrana  propria  of,  70 

mesothelium,  77 

neuro,  77 

pigmented,  76 

pseudo-stratified,  73 

replacing  cells  of,  73 

respiratory,  311 

simple,  71 
columnar,  71 
pseudo-stratified,  73 
squamous,  71 

stratified,  73 
columnar,  74 
squamous,  73 
transitional,  74 

surface,  of  mucous  membranes,  218 

syncytium,  373 

tactile  cells  of,  431 

technic  of,  78 

transitional,  74 
Eponychium,  387 
Epoophoron,  363 
Erectile  tissue,  349,  376 
Ergastoplasm,  213,  272 
Erythroblasts,  192 
Erythrocytes,  103 
Erythrosin,  20 
Eustachian  tube,  574 
Excretory  ducts,  214,  276,  282,  329,  364 

substances  in  ceUs,  46,  213 
Exoplasm,  46,  82 
External  arcuate  fibres,  490,  499 

ear,  572;  see  Ear,  external 

geniculate  bodies,  493,  520 


External  os,  368 

spiral  sulcus,  579 
Extero-ceptors,  436 
Extracellular  network,  139 
Eye,  the,  548;  see  Organ  oj  vision 

blood-vessels  of,  565 

development  of,  569 

eyeball  or  bulbous  oculi,  548 

eyelid,  567 

lacrymal  apparatus,  567 

lens,  564 

lymphatics,  566 

nerves  of,  566 

neurone  systems  of,  560 

optic  nerve,  559 

technic  of,  570 
Eyeball  (or  bulbus  oculi),  548 

blood-vessels  of,  565 

chorioid  of,  550 

ciliary  body  of,  552 

cornea  of,  548 

development  of,  569 

iris  of,  554 

lens,  564 

lymphatics  of,  566 

nerves  of,  555,  559,  565 

retina  of,  555 

sclera  of,  548 

technic  of,  570 
Eyelashes,  567 
Eyelid,  the,  567 

blood-vessels  of,  569 

conjunctiva  of,  568 

epidermis  of,  567 

glands  of,  568 
of  Mall,  568 

lymphatics  of,  569 

Meibomian  glands  of,  568 

muscles  of,  568 

nerves  of,  569 

tarsus  of,  568 

technic  of,  569 

Facialis  (nerve  VII),  474,  47S,  544 
Fallopian  tube,  364;  see  Oviduct 

ampulla  of,  364 

blood-vessels  of,  365 

coats  of,  364 

development  of,  376 

fimbriated  extremity  of,  364 

isthmus  of,  364 

lymphatics  of,  365 


INDEX 


605 


Fallopian  tube,  nerves  of,  365 

ovarian  extremity,  364 

technic  of,  366 
False  corpora  lutea,  360 
Fascicles  of  muscle,  207 

of  nerves,  421,  425 
Fasciculus  arcuatus,  535,  536 

of  Thomas,  467 

inferior  longitudinal,  535 

medial  longitudinal,  467,  485,  491, 
500,  504,  507,  515,  518 

perpendicular  of  Wernicke,  535 

predorsal,  504 

retroflexus  of  Meynert,  53 1 

solitarius,  487,  489 

superior  longitudinal,  535 

uncinate,  535,  536 
Fastigio-bulbar  tract,  500,  502 
Fat,  absorption  of,  273 
technic  of,  275 

blood  supply  of,  91 

development  of,  90 
technic  of,  91 

globules,  237 

osmic-acid  stain  for,  31 

subcutaneous,  382 

tissue,  87 

histogenesis  of,  87 
technic  of,  97 
Fat-droplets  in  cells,  46,  90 
Fat-lobules,  88 

Fauces,  mucous  membrane  of,  220 
Feltwork  of  fibres,  440 
Female  genital  organs,  352 

pronucleus,  59 
Fenestra  ovalis,  574 

rotunda,  574 
Fenestrated  membrane,  94 
Ferrein,  pyramids  of,  320 
Fertilization  of  the  ovum,  58,  358 
Fibrae    propriae    of     Meynert,    535, 

541 
Fibre  baskets,  559 
systems,  421 
eflcrent,  424 
main  motor,  424 
short,  445,  468 
proprio-spinal,  468 
spino-spinal,  468 
tracts  of  cord,  459 

methods  of  determining,  459 
(ascending),  461 


Fibre    tracts   of   cord,   ascending,    direct 

cerebellar,  463 
Gowers',  464 
long  ascending,  445 

arms  of  dorsal  root  fibres,  461 
of  spinal  cord,  459 
posterior  columns,  443,  448 
spino-collicular,  462 
spino-tectal,  465 
spino-thalamic,    462,    483,    501, 

504,  515,  526 
tract  of  Flechsig,  463 
tractus    spino-cerebellaris     dor- 
salis,  463,  483,  487,  490,  507 

ventralis,463, 483, 487, 501,515 
uncrossed   cerebellar,   463,   487, 

49o>  507 
(descending),  464 

anterior     marginal     bundle     of 

Lowenthal,  466 
anterior  pyramids,  464,  483,487, 

504,  507 
antero-lateral,  466 
cerebro-spinalis,  464 
comma  tract  of  Schultze,  467 
crossed  pyramidal,  464 
descending   tract  from   Deiter's 

nucleus,  466 
direct  pyramidal,  465 
fasciculus  of  Thomas,  467 
from  the  interstitial  nucleus  of 

Cajal,  465 
fundamental,  445,  468 
Helweg's,  467 
marginal  bundles  of  Lowenthal, 

466 
origin  of  tracts,  443 
oval  bundle  of  Flechsig,  463 
pallio-spinalis,  464,  533 
pyramidal,  464,  533 
rubro-spinal,  465,  466,  483,  487, 

490,  504,  515 
septo-marginal,  466,  467 
short,  445,  462,  468 
tecto-spinal  tract,  465 
tractus  cortico-spinalis,  464 
vestibulo-spinal,  466 
Von  Monakow's  tract,  466 
Fibres,  afferent  nerve,  419;  see  also  Nerve 
fibres 

arcuate,  487,  489 

association  of  pallium,  421,  533,  535 


606 


INDEX 


Fibres,  calcified,  197 
cartilage,  99 
commissural,  533 
cone,  557 
connective- tissue,  82 

development  of,  82 
cortical,  388 
dentinal,  228 
efferent  root,  418 
enamel,  233 

external  arcuate,  490,  499 
genioglossal,  224 
heart  muscle,  119 
hyoglossal,  224 
intergeminal,  587 

internal  arcuate,  487,  500,  502,  522 
interzonal,  56 
intrageniinal,  587 
involuntary  striated  (heart)  muscle, 

119 
lens,  510,  564 

Mallory's   method   of   staining   con- 
nective-tissue, 29,  30 
mantle,  54 
Muller's,  558 
nerve,  131;  see  also  Nerve  fibres 

meduUated,  133 

non-medullated,  132 
neuroglia,  143 
of  areolar  tissue,  87 
of  bone,  loi 

of  developing  muscle,  124 
of  formed  connective  tissue,  92 
of  Remak,  133 
of  Sharpey,  192,  234 
olfactory,  layer  of,  584 
perforating  or  arcuate,  of  cornea,  550 
projection,  533,  535,  539,  543 
radiate,  292 
reticulo- spinal,  467 
rod,  557 

styloglossal,  224 

superficial  arcuate,  487,  490,  499 
tendon,  91 
tunnel,  583 

voluntary  muscle,  114,  117 
Weigert's  method  for  staining  elastic, 
28 

method  for  staining  nerve,  31 
white  or  fibrillated,  86 
yellow  or  elastic,  86 
Fibrillar  connective  tissue,  86 


Fibrillar  theory  of  protoplasmic  structure, 

44 
Fibroblasts,  82 
Fibrous  cartilage,  99 
Field  of  Forel,  530 
Fila  olfactoria,  475 
Filar  mass,  45 
Filiform  papilla,  225 
Fillet  (or  medial  lemniscus),  462,  485,  487, 

491,  493,  504 
Filum  terminale,  442 
Fimbria,  533 
Fissure,  anterior  median,  448 

chorioid,  570 
Fixation,  5 

by  injection,  6 

in  toto,  6 
Fixatives,  6,  7,  8 
Fixed  cells,  551 
Flechsig,  oval  bundle  of,  467 

myelogenetic  method  of,  459,  541 

tract  of,  463 
Flemming  concerning  cell-division,  53 
Flemming's  fluid,  7 
Foam    theory    of   protoplasm    structure, 

44 
Foetal  cells,  312,  316 

structures,     appendix    epididymidis, 
342 
of  genital  system,  342,  363 
testis,  342 
ductus,  aberrans  Halleri,  342 
organ  of  Giraldes,  342 
paradidymis,  342 
Foliate  papillae,  587 
Follicle,  Graafian,  354;  see  also  Graafian 

follicle 
Follicles,  agminated,  260 

solitary,  253 
Follicular  cavity  or  antrum,  355 
FoUiculi  linguales,  180;  see  Tonsils 
Fontana,  spaces  of,  554 
Foramen  caecum  lingui,  180 
Forebrain  (prosencephalon) ,  417,  522 

diencephalon  {thalamencephalon), 4.17, 
522 
epithalamus,  523 
hypothalamus,  523 
thalamus,  523 
interbrain,  522 

section    through    junction    of    mid- 
brain and  thalamus,  524 


INDEX 


607 


Foregut,  the,  243 

general  structure  of  walls  of  the  gas- 
tro-intestinal  canal,  245 

oesophagus,  243 

stomach,  247 
Forel,  decussation  of,  521 

field  of,  530 
Formaldehyde,  as  a  fixative,  6 

for  macerating,  4 

-bichromate  method,  36 
Formalin,  commercial,  4 
Formahn-Miiller's  fluid  (Orth's),  7 
Formed  connective  tissue,  qi 
Fornix,  531 

anterior  pillars  of,  536 

commissure,  533 
Fossa  navicularis,  352 
Fountain-like  decussation  of  Mej'nert,  522 
Fourth  ventricle,  481,  487,  493 
Fovea  centralis,  559 

Fraenkel's  theorj-  of  corpus  luteum,  362 
Free  endings  of  sympathetic  ner\  es,  441 
Frozen  sections,  15 
Fuchsin,  19 
Function  of  cells,  51 

Fundamental  columns  of  spinal  cord,  445 
Fundus,  248 

glands,  249 
Fungiform  papillae,  225 
Funiculus  cuneatus,  462,  485 

gracilis,  462,  485 

posterior,  461 
Fusiform  lobules,  535 

Gage,  showing  muscle  fibres,  119 
Gage's  hiematoxylin,  17 
Galea  capitis,  343 
Gall-bladder,  295 
Galvanotaxis,  51 
Ganglia,  418,  419 

amphicytes,  427 

cerebral,  426 

cerebro-spinal,  418,  426 

chain,  436 

ciliary,  436 

Gasserian,  506 

habenularis,  530 

of  Corti,  583 

of  Scari^a  of  VIII.,  475,  493 

otic,  436 

peripheral,  436 

satellite  cells,  427 


Gangha,  sphenopalatine,  436 

spinal,  426 

spiral,  583 

spirale  of  VIII.,  475,  493 

structure  of,  426 

sympathetic,  436 

submaxillary,  436 

technic  for,  441 

terminal,  436 

vertebral,  436 
Ganglion  cells,  419 

capsule  of,  419 

cardiac,  162 

development  of,  418 
Gartner's  canal,  377 

duct,  363 
Gasserian  ganglion,  506 
Gastric  crypts,  248 

glands,  248,  249 

pits,  248 
Gastro-hepatic  omentum,  268 
Gastro-intestinal  canal,  general   structure 

of  the  walls  of,  245 
Gelatin,  86 

carmine  for  injecting,  25 

Prussian  blue,  for  injecting,  25 
Gelatinous  marrow,  195 

substance  of  Rolando,  449 
Gemmules,  509 
Geniculate  body,  493,  520,  524 

gangUon  of,  VII.,  474 
Genio-glossal  fibres,  224 
Genital  gland,  378 

organs,  female,  352 
male,  333 

ridge,  378 

system,    333;  see    also    Reproductive 
system 
development  of,  376 
rudimentary  structures  connected 
with  development  of,  342,  363 
Genitourinary  system;  see  Urinary  sys- 
tem, 518,  and  Reproductive  system, 

333 
Gennari,  line  of,  543 
Gentian  violet,  19 
Genu-facialis,  499 
Germ  hill,  356 
layers,  62 

tissues  derived  from,  07 
primitive,  62 
Germinal  epithelium,  354,  378 


608 


INDEX 


Germinal  spot,  357 

vesicle,  59,  357 
Giant  cells  of  Betz,  533,  536 
Gianuzzi,  crescents  of,  222,  278,  302 
Giraldes,  organ  of,  342,  377 
Gland  cells,  212,  213 
Glands,  212 

accessory  thyreoid,  403 

acini  of,  217 

adrenal,  412 

alveolar  saccular,  214 
compound,  217 
simple,  215,  217 

alveoli  of,  217 

Bartholin's,  376 

Bowman's,  300 

Brunner's,  252,  272 

cardiac,  252 

carotid,  410 

cells  of,  212,  213 

ceruminous,  572 

classification  of,  212 

coccygeal,  411 

compound,  214 

corpus  luteum,  359 

Cowper's,  348 

dehiscent,  217 

development  of,  215 

duct,  215 

ductless,  214,  217 

Ebner's,  226 

epithelium  of,  213 

excretory  ducts  of,  214 

fundus,  249 

gall-bladder,  295 

gastric,  249 

general  structure  of,  212 

genital,  378 

giant,  192 

hsemolymph,  173 

internal  secreting,  215,  217 

interstitial  tissue  of,  215 

intraepithelial,  340 

kidney,  318 

lacrymal,  567 

large,  of  digestive  system,   275 

Lieberkiihn's,  252,  260 

lingual,  222 

Littre's,  351,  352 

liver,  287 

lobes  of,  214 

lobules,  214 


Glands,  lymph,  167 
Mall's,  568 
mammary,  395 
Meibomian,  217,  568 
mixed,  221 
mucous,  221 

membranes  of,  218 
of  internal  secretion,  215,  217 
of  the  oral  mucosa,  220 
ovary,  352 
pancreas,  281 
parathyreoids,  404 
parenchyma  of,  215,  277 
parotid,  277 
peptic,  249 
pineal,  544 
prehj^oid,  403 
prostate,  347 
pyloric,  249 
racemose,  21,5 
reticular,  217 
saccular,  217 

compound,  217 

simple,   215 
salivary,  276 

sebaceous,  351,  384,  391,  568,  572 
secreting  portions  of,  213 
serous,  221 
simple,  214 
spleen,  181 
sublingual,  277 
submaxillary,  278 
sudoriferous,  214 
suprahyoid,  403 
sweat,  384,  567 
tarsal,  568 
thymus,  175 
thyreoid,  402 

accessory,  403 
tonsils,  1 78 
tubular,  214,  215 

compound,  216 

simple  branched,  216 

simple  coiled,  216 

simple  straight,  215 
tubulo-alveolar,  214 
tympanic,  409 
Tyson's,  351 
uterine,  367 
Glandulse  sudoriparse,  384 
vestibulares  majores,  376 

mine  res,  376 


INDEX 


609 


Glandular  epithelium,  77,  212 
Glans  penis,  350 
Glenoid  ligaments,  205 
Glisson,  capsule  of,  2S7 
Gliosis,  144 
Globus  major,  334 

minor,  334 

pallidus,  535 
Glomerulus  cf  kidney,  320 

blood-vessels  of,  325 

olfactory,  585 
Glosso-pharyngeal  (IX.  nerve),  474,   491, 

496 
Glycerin  for  mounting  specimens,  22 

jelly,  22 
Glycogen  granules,  290 
Goblet  cells,  75,  212,  257,  272 
Gold  chlorid     for     staining     connective 

tissue  cells,  28 
Gold- size  for  glycerin  mounts,  22 
Golgi  cell,  Tj-pe  I.,  130,  132 

cell,  Type  11.,  131,  132,  446,  536 

method,  bichlorid,  36 
chrome -silver,  29 
Cox  modification,  36 
formalin  bichromate,  36 
mixed,  35 
rapid,  35 

silver,  for  nerve  tissue,  35 
slow,  for  nerve  tissue,  35 

muscle-tendon  organs  of,  434 

net,  139 

organs  of,  434 
Golgi-Mazzoni  corpuscles,  394,  434 
Goll,  column  of,  459,  462 

nucleus  of,  462,  481,  487 
Gowers'  tract,  464 
Graafian  follicles,  354 

antrum  of,  355 

corona  radiata,  356 

cumulus  ovigerus,  356 

development  of,  356,  376 

discus  proligerus,  356 

egg  nest,  354 

epithelium  of,  354 

follicular  cavity  of,  355 

germ  hill  of,  356 

liquor  folliculi,  355 

nerves  oT,  363 

ovum  of,  355 

Pfliiger's  egg  cords,  354 

primitive,  355 
39 


Graafian  follicles,  primitive  ova,  354 

rupture  of,  358 

stratum  granulosum,  355 

technic  cf,  365 

theca  folliculi,  356 

tunica  fibrosa,  356 
vasculosa,  356 
Graded  alcohols,  7 
Grandry,  corpuscles  of,  431 
Granule    theory    of    protoplasmic    struc- 
ture, 40 
Gray  matter,  420,  449 

rami  communicantes,  437 

reticular  formation,  476,  4S5 
Greater  omentum,  235 
Ground  bundles  of  spinal  cord,  445,  468 
Griibler's  methylene  blue,  31,  38 

water-soluble  eosin,  31 
Gums,  mucous  membrane  of,  220 
Gustatory  canal,  587 
Gyrus  dentatus,  532 

hippocampi,  532 

of  Heschl,  541 

Habenul^,  530 
Hffimalum,  Mayer's,  18 
Hasmatein,  17,  104 
Haematoidin,  crystals  of,  360 
Haematokonia,  108 
Haimatoxylin,  17 

and  eosin,  for  staining  double,  20 

and  picro-acid  fuchsin,  21 

Delafield's,  17 

Gage's,  17 

Heidenhain's,  18 

Mallory's  stain,  29 

Weigert's,  19,  32 
Ha;moglobin,  104 
Hajmolymph  nodes,  173 

blood  sinuses  of,  173 

blood-vessels  of,  175 

cells  of,  174 
eosinophiles,  174 
mast  cells,  174 
phagocytes,  174 

development  of,  175 

function  of,  175 

hilum  of,  173 

marrow-lymi)h,  174 

relation  of,  to  lymphatic  system,  175 

spleno-Iymph,  174 

technic  of,  175 


610 


INDEX 


Haemolysis,  104 
Hair,  387 

arrector  pili  muscle  of  the,  391 

blood-vessels  of,  394 

bulb,  387 

-cells,  575,  581 

cells  of  the,  389 

connective-tissue  follicle  of,  389 

cortex  of,  388 

cortical  fibres  of,  388 

cuticle  of,  388 

development  of  the,  358,  395 

excretory  duct  of,  391 

eyelashes,  567 

follicle,  387,  388 

germ,  392 

growth  of  the,  392 

hyaline  membrane,  389 

inner  root  sheath,  388 
cuticle  of,  389 
Henle's  layer  of,  389 
Huxley's  layer  of,  389 

lanugo,  the,  388 

lymphatics,  394 

medulla  of,  387 

nerves  of,  394,  430,  431,  440 

outer  root  sheath,  388 

papilla  of,  387 

prickle  cells,  389 

root  of  the,  387 

root  sheath,  388 

sebaceous  glands  of  the,  391 
sebum  of  the,  392 

shaft  of,  387 

shedding  of  the,  392 

stratum  cylindricum,  389 

technic  of  the,  393 

vitreous  membrane,  389 
Halleri,  ductus  aberrans,  342 
Haller's  layer,  551 
Hamulus,  577 
Hardening,  8 
Hassal's  corpuscles,  177 
Haversian  canals,  189 

development  of,  202 

fringes,  205 

lamellae,  190 

spaces,  202 

systems,  191 

development  of,  202 
Hayem's  fluid,  63 
Head,  sympathetic  ganglia  of,  436 


Headgut,  220 

mouth,  220 

pharynx,  242 

teeth,  227 

tongue,  223 
Hearing,  organ  of,  572;  see  Ear 
Heart,  161 

annuli  fibrosi,  162 

auricular  muscle,  161 

auriculo-ventricular  ring,  161 

blood-vessels  of,  162 

coronary  arteries  of,  161 

development  of,  164 

endocardium  of,  161 

epicardium  of,  161 

lymphatics  of,  162 

muscles  of,  161 

myocardium  of,  140 

nerves  of,  142,  440 

technic  of,  142 

valves  of,  141 

-muscle,  119, 161;  see  also  Involuntary 
striated  muscle 
Hecateromeres,  445 

Heidenhain,  concerning  voluntary  striated 
muscle,  117 

demilunes  of,  222 
Heidenhain's  haematoxyUn,  18 
Heisterian  valve,  295 
HeHcotrema,  578 
Heller's  plexus,  268 
Helweg,  tract  of,  467 
Hemispheres  of  cerebellum,  500,  507 
Hendrickson,   concerning   coats   of  liver 

ducts,  295 
Henle,  concerning  ovum,  ^Ss 
Henle's  layer,  389 

loop,  320,  322,  333 

sheath,  136,  426 
Hensen's  cells,  581 

line,  115 
Hepatic  artery,  289 

cells,  291 

cords,  291 

cyUnders,  297 

duct,  289 
Hermann,  showing  centrosome,  49 
Heschl,  transverse  temporal  gyri  of,  541 
Heteromeres,  445 
Hilum  of  liver,  287 

of  kidney,  318 
Hindbrain,  417,  479 


INDEX 


611 


Hindbrain  {rhombencephalon),  bulb,  479 
cerebellum,  418,  499 
medulla  oblongata,  418,  479 
section  of,  through,  at  level  of  junc- 
tion of  pons  and  cerebellum,  and 
entrance  VIII,  vestibubular,  499 
through    roots    of    VI,    abducens, 

and  VII  facial  nerves,  500 
through    roots    of    V,    trigeminus 
nerve,  502 
His,  marginal  veil  of,  417 
mj^elospongium  of,  417 
spongioblasts  of,  417 
Histogenesis,  67 

Holmgren,  showing   trophospongium,   46 
Horizontal  cells,  538,  558 
Howship's  lacunae,  199 
Huxley's  layer,  389 
Hyaline  cartilage,  98 
Hyaloid  canal,  565 
membrane,  565 
Hyaloplasm,  44,  124 
Hydatid  of  IMorgagni,  342 

stalked,  342 
Hydrochloric  acid  for  decalcif3dng,  10 
Hyoglossal  fibres,  224 

Hypoblast,  62 
Hypoglossal  (XII  nerve),  481,  485,  487, 

497 
Hyponychium,   387 
Hypophysis  cerebri,  407;  see  aLo  Pituilary 

body 
Hypothalamus,  522,  533 

Incisures  of  Schmidt-Latncrmann,  135 
Incremental  lines  of  Schregtr,  232 
Indirect  cell  division,  53;  see  Mitosis 
Inferior  brachium  quadrigeminum,  520 

cerebellar    peduncle;    see    Restijorm 
body 

colliculi,  417 
Infundibula,  310 
Injection,  25 

apparatus,  25 

double,  26 

separate  organs,  26 

whole  animals.  26 
Innervation  of  muscles,  434,  441 
Inokomma,  117 

Interalveolar  connective  tissue,  313 
Intcrarticular  cartilages,  205 
Interbrain,  416,  522 


Interbrain,  epithalamus,  523 
hypothalamus,  523 
thalamus,  523 
Intercallated  discs,  121 
Intercellular  bridges  of  epithelium,  70,  73 
bridges  of  muscle  tissue,  112 
substance,  68 

of  connective  tissue,  86 
silver-nitrate  method  of  staining, 
28 
Interfilar  mass,  45 
Intermediate  cartilage,  199 
lamellje,  191 
neurones,  418 
Internal  arcuate  fibres,  487,  500,  502,  522 
capsule,  530 

ear,  574;  see  also  Ear,  internal 
nuclei  of  cerebellum,  502,  507 
Internode,  134 
Intero-ceptors,  436 
Interradiary  plexus,  541 
Intersegmental  neurones,  421,  483,  487, 
490,  499,  SOI,  504,  507,  515,  520, 
524,  530,  536 
tracts,  468 
Interstitial  lamellae,  191 

nucleus  of  Cajal,  465,  485,  491,  500, 
504 
Intestine;  see  Small  intestine,  255;  Large 

intestine,  263 
Intestines,  development  of,  296 
Intima,  154 

of  arteries,  154 
of  lymph  vessels,  165 
of  veins,  158 
Intracartilaginous  ossification,  199 
Intracellular  canals,  46 
Intrafascicular  connective  tissue,  208 
Intramembranous  ossification,  197 
Intranuclear  network  of  typical  cell,  48 
Inverse  fernient,  273 
Invertin,  273 

Involuntary  striated  muscle  (heart),  119 
Cohnheim's  field,  120 
development  of,  124 
intercallated  discs  of,  121 
McCallum's  views,  120 
membrane  of  Krause,  120 
muscle  columns  of  Kdlliker,  120 
nerves  of,  440 
sarcoplasm  of,  120 
tcchnic  of,  125 


612 


INDEX 


Involuntary  smooth  muscle,  iii 

intercellular  bridges  of,  112 

nerves  of,  440 
Iodine,  to  remove  mercury,  g 
Iris,  the,  554 

greater  arterial  circle,  566 

layers  of  the,  554 

lesser  arterial  circle,  566 

muscles  of  the,  555 

pigmentation  of,  554 
Irriiability  of  cells,  51 
Islands,  blood,  108,  163 

of  Langerhans,  285 
Isolated  smooth  muscle  cells,  113 

technic  of,  124 
Isotropic  line,  115 

substance,  115 
Isthmus,  417,  515 

section    through,     at    exit    of     IV, 
trochlearis,  nerve,  515 
Iter,  417,  464,  515,  517 

Jenner's  blood  stain,  31 
Joint  capsule,  205 

stratum  fiibrosum,  205 
synoviale,  205 

synovial  membrane,  205 
Joints,  204;  see  Articulations 
Jugular  ganglion  of  X,  474 
Juxta-restiform  body,  501 

Karyolysis,  383 

Karyoplasm,  46 

Karyosomes,  48 

Katabolism,  50 

Keratin,  383 

Keratohyaline  granules,  383,  387 

Eadney,  the,  318 

arteriae  arciformes,  326 
rectag,  328 

blood-vessels  of,  325 

Bowman's  capsule  of,  320 

capillaries  of,  328 

columns  of  Bertini,  320 

convoluted  tubules  of,  320 

cortex  of,  318 

cortical  pyramids  of,  320 

development  of,  321,  376 

duct  of  BelUni,  321 

epithelium  of,  324 

glomerulus  of,  320 

Henle's  loop,  322,  323 


Kidney,  interlobar  arteries  of,  326 

hilum,  of,  318 

labyrinths  of,  320 

lobulated,  318 

location  of  tubules  in,  324 

lymphatics  cf,  328 

main  excretory  duct  of,  329 

Malpighian  body,  320 
pyramid,  320 
medulla  of,  318 

medullary    (or     Malpighian)     pyra- 
mid, 320 
rays,  320 

nerves  of,  328 

papillae  of,  321 

pelvis  of,  319 

pyramids  of  Ferrein,  320 

renal  artery.  318 
corpuscle,  320 
vein,  318 

renculi  or  lobes  cf,  318 

septa  renis,  320 

single  lobe  of,  318 

stellate  veins  of  Verheyn,  328 

technic  of,  331 

ureter,  318,  329 

uriniferous  tubule,  320;  see  also  Uri- 
nijerous  tubtde 
Kidney-pelvis,  329 

calyces  of,  329 

development  of,  376 

technic  of,  331 
Kolliker,  muscle  columns  of,  116 

concerning  bronchi,  304 

showing  Golgi  ceU  type  II,  131 
spleen  cells,  184 
Krause,  ellipsoid,  557 

end-bulbs,  227,  350,  394,  567 

line  of,  115 

membrane  of,  117,  120 
Kupffer,  cells  of,  292 

Labia  minora,  sebaceous  glands  of,  384 
Labyrinth,  membranous,  574 

osseous,  574 
Lacrymal  apparatus,  567 
canal,  567 
gland,  567 

blood-vessels  of,  567 
lymphatics  of,  567 
nerves  of,  567 
technic  for,  570 


INDEX 


613 


Lacrymal  apparatus,  nasal  duct  of,  567 

sac,  567 
Lacteals,  240 
Lacuna;,  ici 

origin  of,  198 
Laguesse,     concerning     development    of 
pancreas,  297 
concerning  lung  lobules,  310 
Lamellae,  circumferential,  191 
ground, 191 
Haversian.  19c 
intermediate,  191 
interstitial,  191 
of  bone  tissue,  loi 
Lamina,  bony  spiral,  577 
citrea,  551 
cribrosa,  548,  560 
fusca,  548 

membranous  spiral,  577 
reticularis,  581 
suprachorioidea,  551 
Lamina;  of  cerebellum,  507 
Langerhans,  cell  islands  of,  285 
centro-acinar  cells  of,  283 
centro-tubular  cells  of,  283 
Langley  and  Sewell  ccncerning  secretion, 

272 
Lanugo  hairs,  387 
Large  intestine,  263 

Auerbach's  plexus,  264,  270 
blood-vessels,  268 
coats  of,  263 
development  of,  296 
gland  tubules,  263 
Heller's  plexus  of,  268 
linea;  coli,  264 
lymphatics,  270 
nerves,  270 
plexus  of  Meissner,  263,  271 

myentericus,  270 
technic  of,  275 
Larynx,  the,  301 

blood-vessels  of,  303 
cartilages  of,  301 
arytenoid,  301 
cricoid,  301 
epiglottis,  301 
Santorini's,  301 
thyroid,  301 
Wrisburg's,  301 
cells  of,  301 
development  of,  315 


Larynx,  epithelium  of,  301 
lymphatics,  304 
nerves,  304 
perichondrium,  301 
technic,  304 
vocal  cords,  301 
Law  of  Wallerian  degeneration,  141 
Layer  of  Weil,  228 
Lecithin,  413 
Lemniscus,  bulbo-thalamic,  524 

lateral,  491,  493,  499>  5oi.  504,  5^5 
medial,  462,  485,  487,  491,  493,  504 
Lenhossek,  concerning  ciliated  epithelium, 
Lens,  565 

epithelium,  565 
fibres,  565 

hyaloid  membrane,  565 
invagination,  570 
suspensory  ligament.  565 
vesicle,  571 
zonula  ciliaris,  565 
zonule,  of  Zinn,  565 
Lenticular  capsule,  565 

nucleus,  532,  535 
Leopold,  concerning  pregnant  uterus,  370 
Leucocytes,  105 

acidophile,  106 
basophile,  106 
granular,  106 
lymphocytes,  105 
migratory,  259 
mononuclear,  105 
neutrophile,  106 
of  milk,  400 
polymorphonuclear,  105 
poly  nuclear,  105 
transitional,  105 
Lewis,  concerning  shape  of  blocd-ccUs,  103 
Lieberkiihn,  crypts  of,  252,  260 

glands  of,  252 
Ligament,  glenoid,  205 
spiral,  577 
structure  of,  91 
suspensory,  564 
Ligamcntum  nucha-,  93 

ptctinatum,  554 
Linca;  coli,  264 
Line  of  Gennari,  543 
of  Haillargcr,  54 
Lines  of  Rclzius,  233 
Lingual  glands,  222 
tonsils,  180 


614 


INDEX 


Lingualis,  genio-glossus  fibres  of,  224 
h^'poglossus  fibres  of,  224 
longitudinal  fibres  of,  224 
styloglossus  fibres  of,  224 
transverse  fibres  of,  224 
Linin,  48 

Lipoid  granules,  412 
Liquor  ferri  sesquichlorati,  28 

folliculi,  355 
Lissauer,  zone  of,  443,  450 
Littre,  glands  of,  351,  352 
Liver,  the,  287 

bile  duct  of,  290 
blood  supply  of,  288 
capillary  network,  289 
capsule  of  Glisson,  287 
cells  of,  290 

of  Kupffer,  292 
central  vein  of,  289 
compared     with     other     compound 

tubular  glands,  293 
connective  tissue,  287 
cords  of  liver  cells,  291 
development  of,  297 
ducts,  289 
common,  294 
cystic,  294 
hepatic,  289,  294 
glycogen  granules,  290 
Heisterian  valve,  295 
hepatic  artery,  289 
cords,  291 
duct,  289 
hilum,  287 

intralobular  secreting  tubules,  290 
lobes  of,  287 
lobules,  288 
lymphatics,  294 
main  ducts,  289,  294 
nerves,  294 
portal  canal,  290 

vein,  289 
radiate  fibres,  292 
reticulum,  292 
septa,  287 

sublobular  vein,  289 
technic  of,  297 
tubules  of,  293 
Lobulated  kidney,  318 
Lowenthal,  anterior  marginal  bundle  of, 

466 
Longitudinal  cleavage,  55 


Longitudinal   fasciculus,   491     500,    504, 

515,  526 
Loops  of  Henle,  320,  322,  323 
Loose  (areolar)  connective  tissue,  87 
Lugol's  solution,  28 
Lumbar  enlargement  of  spinal  cord,  443 

segments  of  cord,  443 
Lungs,  the,  308 
air  cells,  310 
sacs,  310 
vesicles,  310 
alveolar  bronchi,  309 
ducts,  310 
passage,  311 
sacs,  309 
alveoli  of,  311 
blood-vessels  of,  313 
bronchial  artery,  313 

system,  313 
capsule  of.  308 
cells  of,  311 
development  of,  315 
epithelium  of,  310 
foetal  cells  of,  311 
infundibula  of,  310 
inter  alveolar  connective  tissue  of,  313 
lobes  of,  308 
lobules  of,  308 
lymphatics  of,  315 
nerves  of,  315 
parietal  pleura,  308 
pulmonary  artery,  308 
lobvde,-3o8 
pleura  of,  308 
respiratory  bronchi,  310 
cells,  311 
epithelium,  311 
septa  of,  308 
technic  of,  317 
terminal  bronchi  of,  310 
Lunula,  387 
Lutein  cells,  359 

granules,  359 
Luteum,  corpus,  359 
Luys,  nucleus  of,  523 
Lymph,  capillaries,  165,  270 

glands,  167;  see  Lymph  nodes 
nodes,  167 

blood-vessels  of,  17c 
capsule  of,  167 
chains  of,  167 
connective  tissue  of,  168 


INDEX 


615 


Lymph  nodes,  cords  of,  169 

cortex  of,  169 

development  of,  171 

germinal  centre  of,  169 

Ij-mphatics  of,  171 

medulla  of,  169 

nen-es  of,  171 

nodules  of,  169 

reticular  connective  tissue  of,  170 

sinuses  of,  169 

technic  of,  172 
nodule,  95,  169,  242,  266 

germinal  centre  of,  169 
paths  of  the  eye,  566 
spaces,  165 

pericellular,  165 

perivascular,  159 
vessel  system,  164 

capillaries  of,  165 

development  of,  166 

lymph  capillaries,  165 
spaces,  165 

relation  of,  to  ha;molymph  node, 

17s 
stomata  of,  165 
technic  of,  165 
vessels,  coats  of,  165 
structure  of,  164 
Lymphatic  organs,  167 

development  of,  171,  i7S>  i77,  180, 

186 
haemolymph  nodes,  1 73 
lymph  nodes,  95,  167 
spleen,  181 

technic  of.  172,  175,  178,  rSi,  187 
thymus,  175 
tonsils,  178 
tissue,  167,  i68 
Lymphocytes,  105 
Lymphoid  cells,  170 
tissue,  170 

Macerating  fluids,  4 
Maceration,  4 
Macrocytcs,  103 
Macro-nucleus,  57 
Macula  acustica,  57S 

lutca,  557 

fovea  centralis,  559 
Male  genital  organs,  333 

pronucleus,  54 
Mall,  glands  of,  568 


Mall,  concerning  development  of  fibrillar 

connective  tissue,  82 
Mallory's  aniline  blue  stain  for  connective 
tissue,  30 
phosphomolybdic  acid  haematoxyUn 

stain  for  connective  tissue,  29 
phosphotungstic    acid    haematoxylin 
stain  for  connective  tissue,  30 
Malpighian  bodies,  182 
body  of  kidney,  320 

development  of,  321,  376 
pyramid,  320;  see  Kidney 
Mamillo-thalaraic  tract,  524 
Mammary  gland,  395 
active,  398 
alveoli  of  active,  398 
ampulla  of,  397 
blood-vessels  of,  400 
cells  of,  398 

colostrum  corpuscles,  400 
development  of,  401 
ducts  of,  397 

of  nipple,  397 
inactive,  397 
interlobar  septa  of,  397 
interlobular  septa  of,  397 
lobular  ducts  of,  397 
lymphatics  of,  400 
milk,  399 
nerves  of,  400 
secretion  of,  399 
structure  of,  395 
technic  of,  401 
Mantle  fibres,  54 

Marchi's  method  for  staining  degen- 
erating nerves,  34 
Busch's  modification  of,  35 
Maresh's   modification  of  Bielschowsky's 

stain  for  connective  tissue,  31 
Marginal  bundle  of  Lowcnlluil,  466 

veil  of  His,  417 
Marrow,  192;  see  Bone  marrow 

lymph  nodes,  1 74 
Martinotti,  cells  of,  536,  539 
Mast  cells,  85,  174,  192.  193 
Matrix  of  nail,  385 
Maturation,  58 

of  ovum,  58,  358 
of  spermatozoon,  58 
Mayer's  hiL-maium,  18 
McCallum,  concerning  heart  muscle,  120 
Media  of  arteries,  155 


616 


INDEX 


Media  of  lymph  vessels,  165 

of  veins,  158 
Medial  eminence,  481,  489 

fillet,  462,  485,  487 
Median  center  of  Luys,  524,  530 
lemniscus,  462,  485,  487,  526 
raphe,  488,  490,  507 
septum,  posterior,  448 
Mediastinum  testis,  333 
Medulla  oblongata,  417,  479 

accessory  olivary  nucleus,  490 

olives,  490 
afferent  cerebellar  neurones,  474,  477, 
490,  493,  SOI,  504,  507 
roots,  483,  485,  489 

secondary   tracts   of,    483,   485, 

489,  491 
terminal  nuclei  of,  483,  485,  489, 
491 
^la  cinerea,  481,  489 
anterior  fissure,  481 

ground    bundles,   483,    487,    489, 

499 
pyramid,  481,  499 

arciform  (arcuate)  mucleus,  490 

arcuate  fibres,  487,  489 

area  acustica,  482 

auditory  nerve,  493 

central  canal,  481 

gelatinous  substance,  487 
gray  matter,  483,  486,  489 
tegmental  tract,  490,  499 

cerebellar  peduncles,  499 

cerebello-olivary  fibres,  490 

chorioid  plexus,  487 

clava,  481 

cochlear  nerve,  475,  489,  491,  493 
nuclei,  493 

column  of  Burdach,  459,  462,  481,  487 
of  Goll,  459,  462,  481,  487 

compared  with  spinal  cord,  481 

corpus  restiforme,  481,  485,  489,  490, 

499,  501,  S04 
crossed  pyramidal  tract,  464,  483 
cranial  nerves  of,  479,  480,  495 
cuneus,  481 
decussation  of  fillet,  485 

of  pyramids,  481 
Deiter's  nucleus,  493,  499 

tract,  487 
descending  root  of  fifth  nerve,  483, 
487 


Medulla  oblongata,  descending  or  spinal 
root    of    vestibular   portion    of 
•     eighth  nerve,  493 
suprasegmental  paths,  485 
tract  from  Deiter's  nucleus,  483, 
491,  499 
from  the  vestibular  nuclei,  490 
development  of,  416 
direct  cerebellar  tract,  483 
pyramidal  tract,  483 
funiculus,  483 
horns,  dorsal,  481 

nucleus  of  ninth  cranial  nerve,  491 
of  tenth  nerve,  481,  485,  489 
dorsal  external  arcuate  fibres,  490 
spino-cerebellar    tract,    483,    487, 
490 
efferent    peripheral    neurones,    483, 
485,  487 
suprasegmental  neurones,  485,  489, 

499 
eminentia  h3^oglossi,  489 
external  arcuate  fibres,  487,  490,  499 
fasciculus  cuneatus,  483 
gracilis,  483 
solitarius,  489,  491 
fillet  or  medial  lemniscus,  462,  485, 

487 
formatio  reticularis,  485,  489,  491 
fourth  ventricle,  481,  487,  493 
funiculus  cuneatus,  485 

gracilis,  485  '        • 

gelatinous    substance    of     Rolando, 

483 
general  structure  of,  479 
genu  facialis,  481 
Gowers'  tract,  483 
gray  reticular  formation,  485,  487 
internal   arcuate  fibres  of,  487,  500, 

502,  522 
intersegmental   neurones,    483,    487, 

489,  499 
lateral  fillet,  491,  493 
lemniscus,  491,  493 
longitudinal      fasciculus,     491,     500 
median  lemniscus,  462,  485,  487,  489, 

491,  493 
longitudinal  fasciculus,  491,  499 
raphe,  488,  490 
nuclei  arcuati,  490 

of  the  floor  of  the  ventricle,  481 
laterales,  490 


INDEX 


617 


Medulla   oblongata,   nuclei  of   posterior 
columns,  481,  495 
nucleus,  abducentis,  482 
accessory  cuneate,  487 
alae  cinereae,  485 
ambiguus,  489 
arcuatus,  490 
commissuralis,  487 
cuneatus,  481,  485,  487 
gracilis,  481,  487 
hjT)oglossi,  481,  485 
of  acoustic  nerve,  482,  489,  493 
of  the  column  of  Burdach,  462,  481, 

487 
of  the  column  of  Goll,  481,  487 
of  the  fifth  spinal  nerve,  483,  485, 

489 
of  origin  of  eleventh  cranial  {spinal- 
accessory)  nerve,  483 
of  origin  of  twelfth  cranial  (hypo- 
glossal) nerve,  481,  485,  487 
of  vagus  nerve,  482,  489 
olives,  489 

olivarj'  nucleus,  487,  490,  491 
olivo-rerebellar  fibres,  49c,  493 
pallio-spinal  tract,  485 
peduncles  of,  499 
peripheral  neurones  of,  479 
plexus  chorioideus,  487 
pons  Varolii,  482,  499 
posterior  columns  of,  487 
longitudinal  fasciculus,  491 
septum,  481 
predorsal  tract,  491 
pyramidal  decussation,  485,  487 

tracts,  485,  487 
raphe,  488,  490 

restiform  body,  481,  485,  489,  490 
reticular   formation,   485,   487,   489, 

490,  491 
root  fibres  of  spinal  V.,  483 

and    nucleus    of    origin    of    sixth 
(abduccns)  cranial  nerve,  499 
of  seventh  (Jacial)  cranial  nerve, 

491 
and  nuclei  of  eighth   (auditory) 
cranial  nerve,  493 
of    ninth    iglosso-pharyngeal)    and 
tenth     (vagus)     cranial    nerves, 
491 
of  eleventh  (spinal-accessory)  cran- 
ial nerve,  483 


Medulla  oblongata,  root  of  twelfth  (hypo- 
glossal) cranial  nerve,  485 
rubro-spinal  tract,  483,  487,  490 
secondary  cochlear  tract,  493 
vestibular  tract,  493 
sensory  tract  of  fifth  nerve,  483, 
487 
section  through  decussation  of  fillet, 

48s 
entrance   of   cochlear  branch  of 

eighth,  491 
lower    part    of   inferior   olivary 

nucleus,  487 
middle      of      oli\-ary      nucleus, 

491 
pyramidal  decussation,  483 
sensory  decussation,  485 
roots  and  motor  nuclei  of  the  fifth 
nerve,  499,  500,  502,  506 
solitary  fasciculus,  489,  491 
spinal     (descending)     root    of    fifth 
cranial  nerve,  483,  487 
V,  475, 483, 4S5, 489, 493, SOI, 504, 
506 
spino-cercbellar      tract,      483,     487, 
489 
-tectal  tract,  483,  490 
-thalamic  tract,  489 
stria;  medullares,  491 
technic  of,  482 
tecto-spinal  tract,  483,  487 
tegmentum,  499 

terminal  nucleus  of   the  descending 
(sensory)  root  fibres  of  the  fifth 
nerve,  483 
tract  of  Gowers,  483 

from  interstitial  nucleus  of  Cajal, 

465 

of  Helwcg,  466,  467 

of  Lciwenthal,  466 
tractus  spinalis  trigcmini,  483 
trapezius,  491 
trigonum  hypoglossi,  481,  489 

vagi,  481 
tubcrculum  cinereum,  481 
ventral  external  arcuate  fibres,  490 

horn,  485,  487 

si)ino-ccrelK;llar  tract,  483 
vestibular  nerve,  475 
vestil)ul()-spinal  tract,  483 
Medullary  lamina,  530 

pyramid  (Maljjighian),  320 


618 


INDEX 


Medullary  rays,  320 

sheath,  134 
MeduUated  axones,  133 

nerve  fibres,  Weigerts'  stain  for,  32 
Megalocytes,  184 
Meibomian  glands,  217,  568 
Meissner,  corpuscles  of,  350,  394,  432 

plexus  of,  254,  262,  263,  271,  436 
Melanin,  131 
Membrana  chorii,  371 

elastica  externa,  156 
interna,  154 

Umitans  olfactoria,  300 

preformativa,  241 

propria,  70 

tectoria,  582 
Membrane,  basal,  70 

cuticular,  71,  240 

mucous,  218 

of  Bowman,  548 

of  Descemet,  550 

of  Krause,  117,  120 

of  Reissner,  579 

peridental,  234 

serous,  165 

synovial,  205 
Membranes  of  brain  and  cord,  422 
Membranous  cochlea,  578 

labyrinth,  574 

spiral  lamina,  S77 
hgament,  577 
Meninges,  422 
Meniscus,  tactile,  431 
Menopause,  401 
Menstrualis,  decidua,  369 
Menstruating  uterus,  368 
Menstruation,  369 
Mercuric  chlorid  as  a  fixative,  8 
Merkel's  corpuscles,  431 
Mesencephalic  root  of  fifth  {trigeminus) 

cranial  nerve,  475 
Mesencephalon,  417 
Mesenchyme,  77 
Mesentery,  268 
Mesoappendix,  265 
Mesobjast,  62 
Mesoderm,  62 

tissue  derivations  from,  68,  122,  296, 

315,377 
Mesonephros,  364 

derivations  from,  342,  364 
Mesothelium,  70,  77 


Metabolism  of  cells,  50,  213 
Metanephroi,  377 
Metaphase,  55 
Metaplasm,  46 
Metathalamus,  523 

Methods  for  studying  fibre  tracts  of  the 
cord,  459 

atrophy,  459 

axonal  degeneration,  459 

comparative  anatomy,  459 

myelogenetic,  459 

physiology,  461 

secondary  degeneration,  459 

von  Guddens,  459 
Methyl  blue,  19 

green,  19 

violet,  19 
Methylene  blue,  38 
Meynert,  decussation  of,  522 

fasciculus  retroflexus  of,  531 

fibrse  propriae  of,  535 

radiations  of,  541 
Micron  (micromillimeter),  15 
Microsomes,  44 
Microtome,  14 
Midbrain,  416,  517 

anterior    corpora    quadrigemina    of, 

S17,  S22 

aqueductus  Sylvii,  517 
basis  pedunculi,  517 
brachia  conjunctiva,  520 
cerebral  peduncles,  517,  521 
coUiculi,  417,  517 
.    corpora  quadrigemina,  417,  522 
cranial  nerves  III.  and  IV.,  520 
crura  cerebri,  518 
decussation  of  Forel,  521 

of  Meynert,  522 
Edinger-Westphal  nucleus,  518 
fourth  cranial  nerve,  520 
geniculate  bodies  of,  520 
inferior    brachium    quadrigeminum, 
520 
coUiculi,  520 
internal  arcuate  fibres,  522 
iter,  517 

lateral  peduncular  fillet,  521 
lemniscus,  462,  520 
medial  accessory  fillet,  521 
mesencephalic  root  of  fifth  nerve,  475 

520 
optic  nerve,  475 


INDEX 


619 


Midbrain,  pes  pedunculi,  521 
posterior  commissure,  522 
corpora  quadrigemina,  517 
longitudinal  fasciculus,  521 
red  nucleus  of,  517,  520,  521 
reticular  formation,  520 
root  fibres  and  nucleus  of  origin  of 
third  {ociiLomotor)  cranial  nerve, 

517 

section  through  exit  of  third  (oculo- 
motor) cranial  nerve,  517 

spino-tectal  tract,  522 

substantia  nigra,  517,  521 

superior  cerebellar  peduncles  of,  521 
collie uU,  520,  522 

tegmentum,  416,  518 
Middle  ear,  573;  see  Ear,  middle 
Midgut,  255 

small  intestine,  255 
Migrator}'  leucocytes,  259 
Milk,  399 

cells  of,  399 

colostrum  corpuscles  of,  400 

teeth,  239,  241 
Minot,  concerning  endothelium  and  meso- 
thelium,  77 

concerning  the  pregnant  uterus,  370 
Mitochondri  a,   213 
Miton,  45 
Mitosis,  53 

anaphase,  56 

metaphase,  55 

method  of  demonstrating  by  Flem- 
ming's  fluid,  8 

prophase,  53 

technic  for,  63 

telophase,  56 
Mitotic  figure,  55 
Mitral  cells,  584 
Mixed  spinal  nerve,  424 
Modiolus,  576 

Mollier,  concerning  splenic  pulp,  185 
Monaster,  54,  55 
Mononuclear  cells,  184 

leucocytes,  105 
Monophylctic  theory  of  blood  cells,  109 
Monosynaptic  arc,  469 
Mordanting,  32 
Morgagni,  hydatid  of,  342 
Mossy  cells,  143 
Motion  of  cells,  51 
Motor  cells  of  anterior  horns,  444 


Motor  decussation,  483 

end  plate,  442 

nuclei,  441 

peripheral  nerves,  441 

precentral  area,  543 
ISIounting,  22 

celloidin  specimens,  23 

in  balsam,  23 

in  glycerin,  22 

paraffin  sections,  23 
Mouth,  the,  220 

blood-vessel  of,  222 

end  bulbs  in  mucous  membrane,  433 

glands  of,  220 

lymphatics  of,  222 

mucous  membrane  of,  220 

nerves  of,  222,  226,  432,  587 

technic  of,  223 
Mucin,  82,  221 
Mucous  glands,  221 

membranes,  218 
end  bulbs  in,  433 
general  structure  of,  218 
of  alimentary  tract,  219 
tactile  cells  of,  431 
corpuscles  of,  432 

tissue,  82 
Mucus,  213,  221 
Muller,  cells  of,  558 

circular  muscle  of,  553 

fibres  of,  558 
Miiller's  fluid,  7 
Miillerian  ducts,  348 
Multinuclear  cells,  184 
Multipolar  nerve  cells,  127,  444 
Muscle,  arrcctor  pili,  391 

auricular,  161 

cells.  III 

ciliary,  553 

circular,  of  Muller,  553 

columns  of  KoUikcr,  116,  117 

discs,  115 

fibrillae,  114 

nuclei,  112 

of  sweat  glands,  395 

spindles,  or  neuro-muscular  bundles, 

434 
tendon  junction,  208,  434 
organs  of  (Jolgi  in,  434 
peripheral   nerve   terminations   in, 

434 
tissue,  III 


620 


INDEX 


Muscle  tissue,  classification  of,  iii 
development  of,  122 
heart,  119 

histogenesis,  119 
intercellular  bridges  of,  112 
involuntary  smooth,  in 

striated,  119 
technic  cf,  124 
voluntary  striated,  114 
anisotropic  substance,  115 
Cohnheim's  fields,  116 
cross  fibre  nets  of,  117 
end  bulbs  of,  434 
ergastoplasm,  114 
Heidenheim's    scheme  of    struc- 
ture of,  117 
Hensen's  Une,  115 
inokomma,  117 
isotropic  substance,  115 
Krause's  line,  115 
mesophragma,  117 
muscle  columns  of  Kolliker,  116, 
117 
discs,  115 
spindles,  434 
nerves,  terminations  in,  434 
Pacinian  corpuscles  of,  434 
Ruffini's  theory  of  nerve  termi- 
nations in,  434 
sarcolemma,  114 
sarcoplasm,  115 

sarcous  element  of  Bowman,  116 
technic  of,  124 
telophragma,  117 
ultimate  fib rillas,  115 
white  and  red  fibres,  117 
Muscles,  voluntary,  207 
capsule  of,  207 
endomysium,  208 
epiraysium,  207 
fascicles  of,  207 
growth  of,  209 
intrafascicular   connective  tissue  of, 

208 
perifascicular  sheath,  208 
perimysium,  208 
Muscular  system,  207 
blood-vessels  of,  210 
lymphatics  of,  210 
nerves  of,  211 
technic  of,  211 
tendons  of,  91,  208 


Muscular  system,  voluntary  muscle,  207 

Muscularis    mucosae    of    mucous    mem- 
branes, 218 

Musculature  of  intestine,  113,  263,  264 

Myelin,  134 

Myeloarchitecture,  541 

Myelocytes,  192 

Myelogenetic    method    for    determining 
fibre  tracts  of  cord,  459,  541 

Myeloplaxes,  193 

Myelospongium  of  His,  417 

Myentericus,  plexus,  270 

Myoblast,  122,  210 

Myocardium,  161 
primitive,  164 

Myofibril,  117 

Myotome,  122 

Myxoedema,  403 

Nabothi,  ovula,  368 
Nails,  the,  385 

cells  of  the,  387 
development  of,  396 
eponychium  of,  387 
growth  of,  387 
hyponychium,  387 
keratohyalin  of,  387 
lunula  of,  387 
matrix  of,  385 
prickle  cells  of,  387 
structure  of,  385 
technic  of,  387 
Nail-bed,  385 
root,  38s 
groove,  385 
wall,  38s 
Nares,  299 

accessory  nasal  sinuses,  299 
cells  of,  30c 

basal,  300 

olfactory,  300 

sustentacular,  300 
development  of,  315 
glands  of  Bowman,  300 
membrana  limitans  olfactoria,  300 
structure  of,  299 

olfactory  region,  299 

respiratory  region,  299 

vestibular  region,  299 
technic  of,  304 
zone  of  oval  nuclei,  300 

of  round  nuclei,  300 


INDEX 


621 


Nasal  duct,  567 

Nemileff,  showing  amitosis,  53 

scheme  of  medullated  nerve  fibre,  137 
Neopallium,  532,  533,  535 
association  fibres  of,  535 
fibrae  of  Meynert,  535 
Ner\-e  cells,  126;  see  also  Neurone 

amacrine,  558,  586 

amphicytes,  427 

anterior  horn,  444 

association,  514,  539 

basket,  222,  510 

Betz',  533,  536,  539 

bipolar,  127,  428 

brush,  585 

Cajal's,  539 

carj^ochromes,  129,  512 

cerebro-spinal  ganglia,  486 

column,  444,  451,  469 

cone-bipolar,  557 

cone- visual,  557 

efferent  projection,  539 

ependymal,  418 

extrinsic,  443 

ganglion,  418,  426,  443,  539 

giant,  of  Betz,  533,  536,  539 

glia,  144 

Golgi,  Type  I,  130,  132 

Type  II,  131,  132,  446,  536 

hecateromeric,  444,  445 

heteromeric,  445 

horizontal,  538,  558 

in  gray  matter  of  cord,  444 

intrinsic,  443 

inverted  pyramidal,  536 

large  granule  cells,  5 1 2 

marginal,  450 

Martinotti's,  536 

mitral,  584 

mossy,  143 

motor,  of  the  anterior  horn,  1 29,  444 

Miillcr's,  558 

multipolar,  127,  444 

neurilemma,  419 

neuroblasts,  126,  142,  418 

neuroglia,  143,  418,  453,  514 

nucleus  of,  127 

of  motor  area  of  cerebral  cortex,  539 

outside  the  spinal  cord,  444 

peripheral  motor,  441 
sensory,  426 

pigment  in,  131 


Nerve  cells,  polymorphous,  536,  530 
Purkinje,  509 
pyramidal,  536 

inverted,  536 
rod-bipolar,  557 
rod- visual,  557 
root,  441,  444,  451 
satellite,  427 
small  granule,  512 
somatochromes,  129 
spider,  143 

spinal  ganglion,  426,  443 
spongioblasts,  143,  417 
stellate,  510,  536 
sympathetic  ganglion,  436 
tautomeric,  445,  463 
unipolar,  127,  428 
endings,    429;    see   Peripheral    nerve 

terminalions 
fibres,  131 
afferent,  419 

root,  420 
association,  421,  533,  535 
climbing,  510,  513 
commissural,  533 
cone,   557 

deep  tangential,  541 
efferent  root,  418 
fastigio-bulbar,  500,  504 
felt  works  of,  440 
layer  of,  of  retina,  558 
lens,  564 
medullated,  133 

of  cerebellum,  5 1 1 
mossy,  513 

motor  end  plates  of,  442 
neuroglia,   143 
non-meduUated,  132 
of  Bergmann,  514 
of  Remak,  133 
of  trapezius,  501 
origin  of,  of  white  matter  of  cord, 

443 
pallial,    533 
pallio-pontile,  501,  504 
])alli<)-tcctal,  535 
pallio-thalamic,  535 
parallel,  of  the  cerebellum,  512 
|)crj)endicular  |)ontile,  499,  501,  507 
l)oslganglionic,  437 
l)reKanglionic,  437 
projection,  533 


622 


INDEX 


Nerve  fibres,  rod  and  cone,  557 
superficial  tangential,  541 
terminations,  430 
motor,  440 
sensory,  430 
tissue,  126 

Golgi  methods  of  staining,  35 
neuroglia,  142 
neurone,  126 
axone,  132 
cell  body,  126 
dendrites,  131 
protoplasmic  processes,  131 
technic  for,  38,  144 
Nerves,  cranial,  table  of,  545,  546 

I  (olfactorius),  475,  532 

II  (opticus),  473,  520,  524,  559 
optic  decussation  of,  526,  561 

chiasma,  526,  561 
tract,  520,  526,  536 
motor  and  sensory  nuclei  of,  421 

III  (oculomotor),  475,  517 
oculomotor  nucleus,  517 

root  fibres  and  nucleus  of  origin 
of  third,  502,  517,  518 

IV  (trochlearis),  475,  515,  518,  520 
root  fibres  and  nucleus  of  origin  of 

fourth,  515,  518,  520 

V  (trigeminus),  475,  485,  489,  493, 
501,  504,  506 

mesencephalic  root  of  fifth,  475, 

506,  515,  520 
motor  nucleus  of  fifth,  504 
"principal  sensory"  nucleus,  506 
semilunar  ganglion  of  fifth,  474 
sensory  nucleus  of  fifth,  506 

and  motor  root  fibres  of  fifth,  506 
spinal  root  of  fifth,  483,  487 
terminal  nucleus  of,  483 
VII  (abducens),  475 
nucleus  of  origin  of  sixth,  499,  500, 
502 

abducentis,  499,  502 
root  fibres  of  sixth,  499,  500,  502 

VII  (facial),  474,  475,  544 
ganglion  geniculate,  474 
nucleus  facialis,  499,  502 

of  origin  of  seventh,  499 
root  fibres  of  seventh,  502 

VIII  (auditory),  475,  481,491,493, 
cochlear  branch  of  eighth,  475,  489, 

491,  493 


Nerves,  ganglion  of  Scarpa,  475,  493 

spirale,  474,  475,  493 
nuclei  of  eighth,  491,  504 
Deiter's,  500,  501 

von  Bechterew's,  493,  507 
root  fibres  of  eighth,  493 
vestibular  branch  of  eighth,  475, 

491,  493 

IX  (glosso-pharyngeal),  474,  491 
descending  or  sensory  root  fibres 

of  the  ninth,  489 
dorsal  nucleus  of  ninth,  491 
ganglia  of,  474 
motor  nucleus  of  ninth,  491 
root  fibres  of  ninth,  491 

X  (vagus),  474,  489 
descending  or  sensory  root  fibres 

of  tenth,  489 
dorsal  nucleus  of  tenth,  481,  485, 

489 
ganglion  jugular,  474 

nodose,  474 
motor  nucleus  of  tenth,  489 
root  fibres  of  tenth,  489 

XI  (spinal  accessory),  483 
nucleus  of  origin  of  eleventh,  483 
root  fibres  of  eleventh,  483 

XII  (hypoglossal),  475,  481 
nucleus  of  origin   of   twelfth,   481, 

485,  487 

root  fibres  of  twelfth,  487,  489 
mixed  spinal,  424 
olfactory,  532 
peripheral,  424 

spinal,    anterior,    motor   or   efferent 
roots  of,  485 

sensory,  or  afferent  portions,  426 
Nervous  system,  the,  416 

cerebro-spinal,  416 

connective  tissue  of,  142 

development  of,  416 

general  structure  of,  416 

sympathetic,  416 
cerebrospinal,  416 

afferent  peripheral  neurones,  424 

brain,  473 

cerebro-spinal  ganglia,  424 

cranial  nerves,  473,  546,  547 

development  of,  416 

efferent  peripheral  cerebrospinal 
neurones,  441 

general  structure  of,  416 


INDEX 


623 


Nervous  system,  histological  development 
of,  416 
membranes  of  brain  and  cord,  422 
segmental  part,  420,  474 
spinal  cord,  442 

ner\-es,  424,  546,  547 
suprasegmental  part,  420,  478 
sympathetic,  416 

development  of,  418 
ganglia,  416,  436 
Neumann's  dental  sheath,  232 
Neural  arc,  421,  469 
cerebellar,  470 
cerebral,  470 
disynaptic,  470 
mono-synaptic,  469 
paUial,  470 

three-neurone,  spinal,  469,  485 
two-neurone,  spinal,  469,  504 
canal,  126 
fold,  416 
groove,  416 
plate,  416 
tube,  416 
Neuraxone,  126 
Neurilemma,  132,  135 

and  axolemma,  relation  of,  136 
-cells,  419 
Neurite,  126 

Neuroblasts,  126,  148,  418 
Neuro-epitheUum,  77 

cone  bipolar  cells,  557 

visual  cells,  557 
rod  bipolar  cells,  557 
visual  cells,  557 
Neurofibrils,  128 

Cajal's  method  of  staining,  37 
importance  of,  in  neurone,  138 
Neuroglia,  142 

mossy  cells  of,  143 
Miiller's  cells  of,  558 
neuroblasts,  126,  142,  418 
of  cerebellum,  514 
spider  cells,  143 
spongioblasts  of,  143 
technic  for,  144 
Neurokeratin  network,  135 
Neurological  staining  methods,  32 
Neuromuscular  bundles,  434 
Neurone,  the,  126 
axonc  of,  132 
canals  in,  131 


Neurone,  caryochromes,  129 
cell  body,  126 
chromophilic  bodies,  129 
contact  theory  of,  138 
continuity  theory  of,  138 
cytoplasm  of,  12S 
degenerative  changes  in,  139 
dendrites  of,  131 
development  of,  126 
extracellular  network  of,  139 
functional  centre  of,  137 
genetic  centre  of,  137 
Golgi  net,  139 
long  axone  neurone,  132 
neurofibrils  of,  127 
Nissl,  special  method  of  technic  for, 

38 
nucleolus,  128 
nucleus,  127 
nutritive  centre  of,  137 
pericellular  network  of,  139 
perifibrillar  substance,  128 
physiological  significance  of,  137 
pigment  in,  131 
protoplasmic  processes,  131 
retraction  theory  of,  138 
short  axone  neurone,  132 
somatochromes,  129 
synapsis  of,  138 
technic  for,  38,  144 
theory,  138 
trophic  centre  of,  137 
Neurones,  aS'ercnt  peripheral,  419,  474 

segmental,  421,  474 

suprasegmental,  421 
associative,  470 
central,  418,  420 
cone  association,  561 
cord,  469 

cortical  precentral,  469 
efferent  peripheral,    segmental,    418, 

441,  474 
suprasegmental,  421,  485 
peripheral  segmental,  421,  474 

intermediate,  418,  420 

intersegmental,  421,  476 

intrascgmental,  421,  476 

pallio-pontile,  501 
peripheral,  419 
afferent,  420,  426,  469,  474 
efferent,  418,  420,  468,  475 

pontocerebellar,  501,  504 


624 


INDEX 


Neurones,  rod-association,  561 

somatic  (peripheral),  419  474,  475 
splanchnic  (peripheral),  419,  474,475 
suprasegmental  associative,  422 
thalamo-cortical  462 
visceral  (peripheral),  419 
Neuroplasm,  134 
Neutral  carmine,  20 
Neutrophile  granules,  106 
Nipple,  397 

Nissl  method  for  staining  nerve  cells,  38 
pathological  value  of,  130 
concerning  chromophilic  bodies,  130 
Nitric  acid  for  decalcifying,  ic 

for  dissociating  muscle  tissue,  5 
Nodes,  lymph,  167 

of  Ranvier,  134 
Nodose  ganglion  of  X  nerve,  474 
Non-medullated  axones,  132 
Normoblasts,  192 
Notochord,  anlage  of,  62 
Nuclear  dyes,  17 

alum  carmine,  19 

basic  aniUn,  19 

carmine,  17 

combination  of  Gage's  and  Mayer's 

formulas,  18 
Delafield's  hsematoxylin,  17 
Gage's  hsematoxylin,  17 
hsematoxylin,  17 
Heidenhain's  hsematoxylin,  18 
Mayer's  hasmalum,  18 
Weigert's  hsematoxylin,  19 
eccentricity,  142 
fluid,  49 
groups,  373 
membrane,  48 
sap,  49 

structures,  method  of  demonstrating 
by  Flemming's  fluid,  7 
Nuclein,  48 
Nucleolus  of  typical  cell,  48 

false,  48 
Nucleoplasm,  49 
Nucleoreticulum,  48 
Nucleus,  the,  47 
abducentis,  502 
accessory  olivary,  490 
alse  cinerese,  485 
ambiguous,  489 
amygdaliformis,  536 
arciform,  499,  530 


Nucleus,  arcuatus,  499,  530 
caudatus,  526,  532,  535 
centralis  superior,  515 
chromatin  of,  48 
commissuralis,  487 
cuneatus,  487 

Deitei's,  466,  476,  483,  500,  502 
dentate,  466,  500,  502,  507 
dorsal  cochlear,  493 
Edinger-Westphal,  518 
emboliformis,  502,  507 
facialis,  499 

fastigii,  466,  SCO,  502,  507 
function  of,  47 
funiculi  cuneati,  462,  485 

gracilis,  462,  485 
globosus,  502,  507 
hypoglossi,  485 
interstitial,  of  Cajal,  465,  485,  491, 

50O)  504 
karyoplasm  of,  49 
lenticularis,  532,  535 
linin  of,  48 
mediaUs,  490 
membrane  of,  48 
network  of,  48 
nuclein  of,  48 
nucleoreticulum  of,  48 
nucleolus  of,  48 
oculomotor,  518 
of  acoustic  tubercle,  493 
of  a  typical  cell,  47 
of  column  of  Burdach,  462,  481,  487 

of  Goll,  462,  481,  487 
of  Darkschewitsch,  465 
of  Luys,  523 
of  origin,  421 
oculomotor,  518 
olivary,  487,  490,  491,  500,  507 
pontis,  504 
preolivary,  500 
pulposus,  204 

red,  436,  466,  476,  5x7,  524 
resting,  57 

reticvdaris  tegmenti,  504 
ruber,  436,  466,  476,  517,  524 
semilunar,  500 
tecti,  466,  500,  502 
terminal,  421,  490 
trapezoid,  491,  500,  507 
triangular,  490 
ventro-lateral,  530 


INDEX 


625 


Nucleus,  vestibular,  490,  493,  500 

von  Bechterew's,  500,  507 
Nuel's  space,  5S1 
Nutrient  canal,  196 

foramen,  196 

vessels,  of  bone,  196 
Nutritive  center  of  neurone,  137 

Oculomotor  III  nerve,  517,  518 

nucleus,  5x7,  518 
Odontoblasts,  228,  241 
CEsophagus,  the,  243 

technic  of,  215 
Oil    of    origanum    Cretici     for     clearing 

specimens,  23 
Olfactorius  (I  nerve),  475,  532 
Olfactory  bulb,  532,  585 
granule  laj'er,  586 

of  longitudinal  fibre  bundles,  586 
of  mitral  cells,  586 
of  olfactory  fibres,  586 
molecular  layer,  586 
olfactory  glomeruli  of,  586 
path,  475,  532,  533,  539 
pallial  commissure,  533 
group  of  segmental  neurones,  475 
nerve,  475,  532 
organ,  584 
pallium,  532 
tract,  475,  539,  586 
Ohvary  nucleus,  481,  487,  493,  500,  507 
Olives,  487,  489,  491,  493,  501 
Omentum,  268 

gastro-hepatic,  268 
greater,  268 
Opie,  concerning  the  pancreas,  286 

concerning  the  cell-islands  of  Langer- 
hans,  286 
Oppel's  method  of  staining  intralobular 

connective  tissue  of  liver,  296 
Optic  chiasma,  526,  561 
cup,  570 
decussation,  561 
depressions,  569 
nerve,  475,  520,  524,  559 
arachnoid  of,  560 
dural  sheath  of,  559 
pial  sheath,  559 

relation  to  retina  and  brain,  560 
subarachnoid  space,  5O0 
subdural  space,  5O0 
technic  of,  570 
40 


Optic  stalk,  569 

tract,  S20,  524,  536 
vesicle,  569,  570 
Opticus  (II  nerve),  473 
Ora  serrata,  552,  555 
Oral  glands,  cells  of,  220 

crescents  of  Gianuzzi,  222 
demilunes  of  Heidenhain,  222 
mixed  glands,  221 
mucous  glands,  221 
serous  glands,  221 
technic  of,  223 
Orange  G,  20 
Organ  of  Corti,  580 

acoustic  neurones  to,  475 
cells  of  Claudius  of,  581 
Corti's  arches,  581 

tunnel,  581 
Deiter's  cells,  581 
hair  or  auditory  cells,  581 
Hcnscn's  cells,  581 
lamina  reticularis  of,  581 
Nuel's  space  of,  581 
phalangeal  processes,  581 
pillar  cells,  580 
of  Giraldes  (paradidymis),  342,  377 
of  hearing,  572;  see  also  Ear 
blood-vessels  of,  582 
development  of,  583 
ear,  external,  572 
internal,  574 
middle,  573 
lymphatics,  582 
nerves,  582 
technic  of,  584 
of  smell,  584;  see  Oljaclory  organ 
olfactory  bulb,  -85 
mucosa,  584 
tract,  586 
technic  of,  586 
of  taste,  587 
cells  of,  587 
foUatc  pai)illa;,  587 
gustatory  canal,  587 
intergeminal  fil)rcs  of,  587 
intrageminal  fibres  of,  587 
taste  buds,  226,  227,  432,  433,  587 
technic  of,  587 
of  vision,  548 

lilood-vesscis  of,  565 
development  of,  5(19 
eyeball  or  bubus  oculi,  548 


626 


INDEX 


Organ  of  vision,  eyelid,  567 

lacrymal  apparatus,  567 
lens,  564 

lymphatics  of,  566 
nerves  of,  566 
neurone  systems  of,  560 
optic  nerve,  473,  520,  524,  559 
technic  of,  570 
of  Zuckerkandl,  412 
Organs,  the,  149 

circulatory  system,  151 
digestive  system,  219 
acoustic  neurones  to,  475 
glands,  duct,  212 

ductless,  402 
lymphatic  organs,  167 
muscular  system,  207 
nervous  system,  416 
reproductive  system,  333 
respiratory  system,  299 
skeletal  system,  188 
skin  and  its  appendages,  380 
special  sense  organs,  548 
urinary  organs,  318 
of  special  sense,  548 
organ  of  hearing,  572 
of  smell,  584 
of  taste,  587 
of  vision,  548 
Organs  of    Golgi,    peripheral    nerve    ter- 
minations in,  434 
Orth's  fluid  (f or malin-M tiller's),  7 
Osmic  acid  as  a  fixative,  8 
action  on  fat,  8 
on  myelin,  8 
stain  for  fat,  31 
Osseous  labyrinth,  574 
Ossicles  of  middle  ear,  574 
Ossification,  82 
centres,  197 
endochondral,  199 
intracartilaginous,  199 
intramembrancus,  199 
subperichondral,  199 
subperiosteal,  199 
Osteoblasts,  198,  235 
Osteoclasts,  199,  235 
Osteogenetic  tissue,  197 
Otic  ganglion,  436 

vesicle,  583 
Otocyst,  583 
Otolithic  membrane,  575 


Otoliths,  575 

Oval  bundle  of  Flechsig,  467 

Ovary,  the,  352 

blood-vessels  of,  363 

corpora  lutea,  of  pregnancy,  360 
spuria,  360 
vera,  360 

corpus  albicans,  360 
haemorrhagicum,  359 
luteum,  359 

cortex  of,  353 

development  of,  376 

egg  nest,  354 

epoophoron,  ^('S 

Fallopian  tube,  353,  364 

germinal  epithelium  of,  354 

Graafian  follicles,  354 

haematoidin  crystals,  360 

hilum  of,  353 

lutein  cells,  359 

lymphatics  of,  363 

medulla  of,  353 

nerves  of,  363 

ovarian  stroma,  353 

oviduct,  353 

ovum,  352,  3SS 

paroophoron,  363 

Pfliiger's  egg  tubes  or  cords,  354 

primitive  ova,  354,  378 

rudimentary     structures     connected 
with,  363 

secretion  of,  352 

structure  of,  353 

technic  of,  365 

tunica  albuginea,  353 

zona  vasculosa,  353 
Oviduct,  the,  364;  see  Fallopian  tubes 
Ovula  Nabothi,  368 
Ovum,  the,  52,  355,  356 

atresia  of  follicle,  363 

cells  of,  357 

deutoplasm  granules,  357 

development  of,  356 

fertilization  of,  58,  358 

germinal  spot,  357 

maturation  of,  357 

perivitelline  space,  357 

primitive,  378 

segmentation  of,  62 

yolk  granules  of,  357 

zona  peUucida  of,  357 
Oxyhfemoglobin,  107 


INDEX 


627 


Oxyntic  cells,  249 
Oxj-phile  cells,  405 

Pacchionian  bodies,  424 
Pacinian  bodies,  196,  433 

corpuscles,  350,  434 
Palate,  mucous  membrane  of,  220 
Palatine  tonsils,  178;  see  Tonsils 
Pallial  connections,  461, 462, 464, 469, 470, 

477,  522 
Pallio-pontile  fibres,  501,  504,  517 
Pallio-ponto-cerebellar  path,  501 
Pallio-spino-peripheral    efferent    conduc- 
tion path,  465 
Pallio-thalamic  fibres,  523,  535 
Pallio-tectal  fibres,  535 
Pallium,  417,  532,  536 

cortical  areas  of,  536 

fibres  of,  533 
Pancreas,  the,  281 

blood-vessels  of,  286 

cell-islands  of  Langerhans,  285 

centro-acinar  cells  of  Langerhans,  283 

development  of,  295 

duct  of  Santorini,  282 
of  Wirsung,  281 

ductus  choledochus,  295 

excretory  ducts,  282 

intracellular  secretory  tubules  of,  285 

lobules  of,  281 

lymphatics  of,  286 

nerves  of,  286 

Opie,  concerning  cell-islands,  286 

secondary  excretory  duct  of,  286 

secretion  of,  285 

sustentacular  cells  of,  284 

technic  of,  287 

terminal  tubules  of,  282 

zymogen  granules  of,  282 
Paneth,  cells  of,  260,  273 
Panniculus  adiposus,  383 
Papilla;,  circum vallate,  225,  587 

compound,  381 

filiform,  225 

foliate,  587 

fungiform,  225,  587 

nerve,  381 

of  mouth,  220 

pharynx,  242 

simple,  381 

vascular,  383 
Paradidymis,  or  organ  of  f  iirald^s,  342, 377 


Paraffin  embedding,  13 
apparatus  for,  14 

oven,  13 

section-cutting,  15 

sections,  staining  and  mounting  of,  23 
Paraganglia,  409 

carotid  gland,  410 

chromaflin  organs,  410 

coccygeal  gland,  411 

organ  of  Zuckerkandl,  412 

tympanic  gland,  412 
Paralinin,  48 
Paramiton,  45 
Paranuclein,  48 
Paranucleus,  213 
Paraplasm,  46 
Parathyreoids,  404 

chief  or  clear  cells  of,  405 

development  of,  406 

function  of,  406 

oxyphile  cells,  405 

Pool's  theory  of,  406 

technic  of,  406 
Pareleidin,  384 

Parenchyma  of  glands,  215,  277 
Parietal  cells,  249 

peritoneum,  267 

pleura,  308 
Paroophoron,  363 
Parotid  gland,  277 

development  of,  297 

intercalated  tubule  of,  267 

nerves  of,  280 

Stenoni's  duct  of,  277 

technic  of,  281 
Pars  ciliaris  retina;,  555,  559 

iridica  retina;,  555,  559 

optica  retinae,  555 

papillaris,  381 

reticularis,  380 
Pavlow,  concerning  secretion,  273 
Peduncle,  inferior,  499,  500 

middle,  499 

superior,  499,  500,  502,  507,  517 
Pellicula,  47 
Pcnicillus,  183 
Penis,  349 

arteries  of,  350 

cavernous  sinuses,  350 

corpora  cavernosa  of,  349 

corpus  spongiosum  of,  349 

erectile  tissue,  349 


628 


INDEX 


Penis,  glans,  350 

glands  of  Tyson  of,  351 

lymphatics,  350 

nerve  endings  of,  350 

prepuce  of,  351 

sebaceous  glands  of,  351 

technic  of,  352 

tunica  albuginea  of,  349 
Pepsinogen  granules,  272 
Peptic  cells,  249,  272 

glands,  249 
Perforated  space,  anterior,  536 
Perforating  fibres,  192 

of  cornea,  550 

of  Sharpey,  192 
Perforatorium,  343 
Periaxial  sheath,  134 
Pericardial  cavity,  165 
Pericellular  network,  139 
Perichondrium  of  bone,  199 

of  cartilage,  99 
Perichoiioidal  lymph  spaces,  551 
Pericranium,  198 
Peridental  membrane,  234 
Perifascicular  sheath,  208,  425 
Perifibrillar  substance,  128 
Perilymph,  574 
Perimysium,  208 
Perineurium,  425 
Periosteal  buds,  200 
Periosteum,  191,  199 
Peripheral    afferent    neurones,    419,  426, 

474 

cerebro-spinal  ganglia,  426 

symphathetic  ganglia,  436 
efferent  neurones,  420,  441,  475 
motor  neurone  system,  441 
nerves,  419,  424 

afferent  part  of,  424 

cranial,  424 

efferent  part  of,  424 

endoneurium  of,  425 

epineurium  of,  425 

fascicles  of,  425 

intrafascicular  connective  tissue  of, 

425 
medullated  fibres  of,  133 
motor  or  efferent,  424 
motor  nerve  terminations,  441 
non-meduUated  fibres  of,  132 
perifascicular  sheath  of,  425 
perineurium  of,  425 
sensory  or  afferent,  424 


Peripheral  nerves,  sensory  nerve  termina- 
tions, 429 

sheath  of  Henle,  426 

spinal,  424 

structure  of,  424 

technic  of,  426 
nerve  terminations,  429 

annular,  434 

diffuse,  430 

end-bulbs,  431,  433 

free  endings,  430 
in  penis,  350 

golgi  Mazzoni  corpuscles,  394,  434 

grandry,  corpuscles,  431 

in  mucous  membrane  of  mouth  and 
conjunctiva,  432 

in  muscle-tendon  junctions,  434 

in  skin,  394,  430 

in  smooth  muscle,  430 

in  voluntary  muscle,  434 

Krause's  end-bulbs  in  penis,  350 

Meissner's  corpuscles  in  papillae  of 
penis,  350 

muscle  spindles,  434 

muscle-tendon  organs  of  Golgi,  434 

neuromuscular  bundles,  434 

Pacinian  bodies,  196,  433 
corpuscles  of  penis,  350 

nerve  terminations,  Ruf&ni's  theory 
of,  434 

spiral  terminations,  434 

tactile  cells,  431 
corpuscles,  432 
meniscus,  431 

taste  buds,  432 
Peripheral  nervous  system,  416 

spinal  nerves,  424 
Peritoneal  cavity,  165 
Peritoneum,  267 

parietal,  267 

subserous  tissue  of,  268 

visceral,  267 
Perivitelline  space,  357 
Permanent  teeth,  239,  242 
Perpendicular  fasciculus  of  Wernicke,  535 

pontile  fibres,  499,  501,  507 
Pes  pedunculi,  417,  517,  521,  526,  530,  536 
Petit,  canal  of,  565 
Petrosal  ganglion  of  IX,  474 
Peyer's  patches,  260 
Pfliiger's  egg  tubes  or  cords,  354 
Phaeochrome  granules,  412 
Phaeochromoblasts,  415 


INDEX 


629 


Phagocytes.  107,  174 
Phagocytosis,  107 
Phalangeal  processes,  581 
PharjTigeal  tonsils,  180;  see  Tonsils 
Phan-nx,  the,  242 

blood-vessels  of,  243 
lymphatics  of,  243 
nerves  of,  243 
structure  of,  242 
technic  of,  243 
Phloroglucin,  10 
Pia  mater,  422 

arachnoid,  422 
blood-vessels  of,  424 
cereb rails,  422 

Pacchionian  bodies,  424 
spinalis,  422 
technic  of,  424 
Picric  acid  as  a  fixative,  8 

as  plasma  dye,  20 
Picro-acid-fuchsin,  20 
Picro-carmine,  21 
Pigment  granules  in  cells,  46,  384 
in  connective  tissue,  87 
in  epithelium,  76 
hair,  388 
in  iris,  554 
in  nerve  cells,  131 
Pillar  cells,  581 
Pineal  body,  544 

brain  sand  of,  547 
technic  of,  547 
Pineal  eye,  544 
Pinna,  572 
Pituitary  body,  407 

Berkley,  concerning  posterior  lobe, 

408 
function  of,  409 
relation  of,  to  pregnancy,  409 
technic  of,  408 
Placenta,  371 

blood-vessels  of,  374,  375 
canalized  fibrin,  373 
cell  patches,  373 
chorionic  villi,  371 
cotyledons,  371 
fastening  villi,  371 
foctalis,  371 

free  or  floating  villi  of,  371 
lymphatics  of,  375 
membrana  chorii  of,  371 
nerves  of,  37S 


Placenta,  nuclear  groups,  373 

septa  of,  374 

subchorionic  placental  decidua,  374 

syncytium  of,  373 

technic  of,  379 

uterina,  373 

villi  of,  371 
Plasma  cells,  193 
Plasma  dyes,  17,  19 

acid  aniline,  20 

eosin,  19 

neutral  carmine,  20 

picric  acid,  20 
Plasmosome,  48 
Plastids,  46 
Plastin,  44 
Platelets,  blood,  108 
Pleura,  parietal,  308 
pulmonary,  308 
Pleural  cavity,  165 
Pleuroperitoneal  cleft,  165 
Plexiform  layer  of  Cajal,  538 
Plexus  annularis,  567 

Auerbach's  264,  270,  436 

ciliary,  566 

chorioideus,  417,  482,  487,  502 

Heller's  268 

interradiary,  541 

Meissner's,  254,  262,  263,  271,  436 

myentericus,  270 

prevertebral,  436 

supraradiary,  541 
Plicae  palmata^,  368 

Pncumogastricus  (vagus  nerve),  474,  489 
Polar  bodies,  59,  358 
globules,  61 
rays,  54 
Polykaryocytes,  193 
Polymorphonuclear  leucocytes,  105 
Polym()ri)h()us  cells,  105 
Polynuclear  leucocytes,  105 
Pons  Varolii,  17,  482,  499,  501,  515 
longiUidinal  fibres  of,  499,  501 
pcr|)fn<li(  ular  fibres,  499,  501,  507 
pontile  nuclei  of,  501 
pyramid  of,  501 
transverse  fibres  of,  501 
Pool,    E.    II.,    concerning    p:ir.ithyrc<)id 

gland,  406 
Poroyi)horon,  363 
Portal  canal,  290 
vein,  289 


630 


INDEX 


Posterior  columns  of  spinal  cord,  443,  448 
origin  of  fibres  of,  443 

column  of  Burdach,  459,  462,  485 
of  Goll,  459,  462,  485 

commissure,  522,  526 

corpus  quadrigemium,  493,  517 

distribution  of  fibres  of,  452 

funiculus,  448,  461 

horns,  445,  448 

longitudinal  fasciculus,  491 

median  septum,  448 

nerve  root,  450 
root  fibres,  450 

nucleus  funiculi  cuneati,  462,  485 
funiculi  gracilis,  462,  485 
of  the  column  of  Burdach,  462,  485 
of  the  column  of  Goll,  462,  485 

origin  of,  443 

tract,  or  terminal  zone  of   Lissauer, 

443,  450 
zone  of  Lissauer,  443 
Potassium  hydrate,  as  a  macerating  fluid, 

4 
Precapillary  artery,  154 
Predorsal  fasciculus,  504 
Prepuce,  351 
Preparation  of  sections,  5 
Preserving,  9 

Prevertebral  plexuses,  436 
Prickle  cells,  383,  387 
Principal  sensory  nucleus  of  nerve  V,  506 
Projection  fibres,  533 
Pronephric  or  Wolffian  ducts,  377 
Pronephroi,  376 
Pronucleus,  female,  59 

male,  59 
Prophase,  53 
Proprio-ceptors,  436 
Proprio-spinal  tract  of  cord,  468 
Prosencephalon,  416,  522 
Prostate  gland,  347 

blood-vessels  of,  348 

capsule  of,  347 

corpora  amylacea  of,  348 

crescentic  corpuscles  of,  348 

epithelium  of,  317 

lymphatics  of,  348 

Miillerian  duct,  348 

nerves  of,  348 

technic  of,  349 

trabeculas,  347 

uterus  masculinus,  348 


Prostate  gland,  utriculus  prostaticus,  348 

vesicula  prostatica,  348 
Protargol,  for  staining  intercellular  sub- 
stance, 28 
Protoplasm.  43,  45 

streaming  of,  52 

theories  of  structure  of,  44 
Protoplasmic  movement,  52 

processes,  131 
Proximal  convoluted  tubule,  319 
Prussian  blue  gelatin  as  an  injecting  fluid, 

Pseudochromosomes,  213 
Pseudopodia,  50 
Pulvinar  radiations,  524 

thalami,  524 
Pulmonary  artery,  313 

lobule,  308,  313 

pleura,  308 
Pulp  cavity,  227 

cord,  184 

splenic,  184 
Purkinje  cells,  509 
Putamen,  535 
Pyloric  glands,  252 
Pylorus,  252 
Pyramid,  cortical,  320 

of  Ferrein,  320 

Malpighian,  320 
Pyramidal  cells,  536 

decussation,  464,  485 

tracts,  464 

anterior  pyramids,  464,  483,  487, 

504,  507 
crossed  pyramidal,  464 
direct  pyramidal,  465 
pyramidal  decussation,  464 

Pyramids,  417,  504,  507,  S^S 

P5T:enin,  48 

Pyriform  lobe,  532 

Racemose  glands,  215 
Radiations  of  Meynert,  541 
Radix  spinalis,  V,  483,  487 
Rami  communicantes,  gray,  437 

white,  425,  436 
Ranvier's  alcohol  as  a  macerating  fluid, 

4 
nodes  or  constrictions  of,  134 
showing  muscle  fibres,  115 
Raphe,  of  semicircular  canals,  576 
median,  488,  490,  507 


INDEX 


G31 


Receptors,     419,     424,     425,     429, 
436 
extero-ceptors,  436 
intero-ceptors,  436 
proprio-ceptors,  436 
Sherrington's  classification  of,  436 
Rectum,  266 
anus,  267 

columnae  rectales,  266 
technic  of,  275 
Red  blood  cells,  103;  see  also  Blood 
nucleated,  109,  192 
nucleus,  436,  466,  476,  517 
Reduction  of  chromosomes,  55,  344 
Reflex  arc,  disj-naptic,  470 
monosynaptic,  469 
three-neurone  spinal,  469 
two-neurone  spinal,  469 
Reissner,  membrane  of,  579 
Remak,  fibres  of,  133 
Renal  corpuscle,  320 

development  of,  320,  377 
Renculus,  318 
Replacing  cells,  73,  252 
Reproduction  cells  of,  52  ^ 

Reproductive  system,  2^;^ 
development  of,  376 

rudimentary  structures  connected 
wath  the,  342,  363 
female  organs,  352 
clitoris,  376 
Fallopian  tube,  364 
ovary,  352 
oviduct,  364 
placenta,  371 
urethra,  351 
uterus,  366 
vagina,  375 
vestibule,  376 
male  organs,  333 

Cowper's  glands,  348 
ejaculatory  ducts,  341 
penis,  349 
prostate  gland,  347 
seminal  ducts,  339 

vesicle,  341 
seminiferous  tubule,  334 
spermatozoa,  343 
testis,  333 
urethra,  351 
Respiratory  bronchus,  310 
cells,  3 1 1 


Respiratory  epithelium,  311 

system,  299 

bronchi,  304 

development  of,  315 

larynx,  301 

lungs,  308 

nares,  299 

technic  of,  304,  317 

trachea,  301 
Restiform  body,  4S1,  485,  489,  490,  499, 

501.  504 
Rete  testis,  tubules  of,  334,  339 

vasa  efferentia,  339 
Reticular  formation,  476,  485,  487,  489, 
490,  491,  501,  504,  507 
glands,  217 
process,  448,  455 
tissue,  170 
Reticulin,  95 
Retina,  555 

blood-vessels  of,  565 
ellipsoid  of  Krause,  557 

fibre-basket  of,  559 
fovea  centralis,  559 
ganglionic  layer  of,  555 
horizontal  cells  of,  558 
inner     limiting      membrane      of, 

558 
molecular  layer,  557,  558 
nuclear  layer,  557 
layer  of  nerve  cells,  558 
of  nerve  fibres,  558 
of  neuro-epithelium,  555,  556 
of  pigmented  epithelium,  555 
of  rods  and  cones,  556 
macula  lutea,  559 
Miillcr's  cells  and  fibres,  558 
ora  scrrata,  555 
outer  limiting  membrane,  558 
molecular  layer,  558 
nuclear  layer,  556 
I)ars  ciliaris  retina;,  555,  559 
iridica  retina;,  555,  559 
optica  retina;,  555 
relation  to  optic  nerve,  560 
rod  and  cone  cells  of,  557 
visual  purple  of,  557 
Rctinacuhe  cutis,  387 
Retraction  hyi)Othcsis,  138 
Kclrolcnticuiar  portion   of   inlcrnal   cap- 
sule (('irl),  526 
Rctzius,  lines  of,  233 


632 


INDEX 


Rhinencephalon,  417,  532 
Rhinopallium,  532 
Rhombencephalon,  417,  479 
Ribboning  parafSn  sections,  15 
Rod  association  neurones,  561 

fibres,  557 

neurones,  560 
Rod- visual  cells,  557 
Rods,  layer  of  rods  and  cones,  557 
Rolando,  gelatinous  substance  of,  449 
Root  canal,  228 

cells,  441,  444,  451 
Roots,  afferent,  419 
Rose  concerning  chromaffin  cells,  410 
Rufi&ni,  corpuscles  of,  394 

theory  of  nerve  terminations,  434 
Rugas,  246,  248,  295 

Riihle,  concerning  the  uriniferous  tubule, 
325 

Saccular  glands,  215,  217 
Saccule,  and  utricle,  575 
auditory  hairs  of,  575 
macula  acustica,  575 
neuro-epithelial  cells  of,  575 
otolithic  membrane  of,  575 
otoliths  of,  575 
sustentacular  cells  of,  575 
Sachs,  E.,  concerning  thalamus,  523 
Sacral  segments  of  spinal  cord,  458 
Safranin,  19 
Salivary  corpuscles,  180 
glands,  276 
blood-vessels  of,  278 
development  of,  297 
lymphatics  of,  280 
minute  structure  of,  221 
nerves  of,  280 
parenchyma  of,  277 
parotid,  the,  277 
sublingual,  the,  277 
submaxillary,  the,  278 
technic  of,  281 
Santorini,  cartilage  of,  301 

duct  of,  282 
Sarcolemma,  114 
Sarcoplasm,  114 
Sarcostyles,  209 

Sarcous  elements  of  Bowman,  116 
Satellite  cells,  427 
Scala  media,  578 
tympani,  578 


Scala  vestibuli,  578 
Scarpa's  ganglion,  475,  493 
Schaper,  concerning  placenta,  371 
Schlemm,  canal  of,  554 
Schmidt-Lantermann,  clefts  of,  135 

incisures  of,  135 

segments  of,  135 
Schreger,  lines  of,  232 
Schultze,  comma  tract  of,  467 
Schwalbe,  lymph  paths  of,  566 
Schwann,  sheath  of,  132,  135 
Sclera,  the,  548 
Scrotum,  skin  of,  333 
Sebaceous  glands,  384,  391 

development  of,  395 

of  glans  penis,  351,  384 

of  labia  minora,  384 

of  margin  of  hps,  384 

of  prepuce,  384 
Sebum,  392 
Secondary  cochlear  tract,  493,  504,  507 

trigeminal  tract,  483 

vestibular  tract,   493 
Secretion,  42,  213,  271 
Secretory  tubules,  276 

Golgi  method  of  demonstrating,  29 

of  parietal  cells  of  stomach,  251 
Section  cutting,  14 

celloidin  specimens,  14 

frozen  sections,  15 

paraffin  specimens,  14 

staining,  17,  20 
Segmental  brain,  420,  474 

nerves,  420,  474 

paths,  476 
Segmentation  cavity,  61 

of  ovum,  62 
Segments  of  Schmidt-Lantermann,  135 

of  spinal  cord,  448,  455 
Semen,  343 

Semicircular  canals,  473,  576 
crista  acustica  of,  576 
cupula  of,  576 
raphe  of,  576 
semilunar,  fold  of,  576 
Seminal  ducts,  339 

vas  epididymis,  340 
vas  deferens,  340 
vasa  efferentia,  339 

vesicles,  341 
Seminiferous  tubules,  334 

cells  of,  335 


INDEX 


633 


Seminiferous  tubules,  columns  of  Sertoli, 
335 

convoluted  portion  of.  334 

development  of,  344 

glandular  cells  of,  335 

rete  testis,  334,  339 

spermatids,  337 

spermatocytes,  337 

spermatogenic  cells,  335 

spermatogones,  336 

spermatozoa,  337 

straight  portion  of,  338 

supporting  cells  of,  335 

sustentacular  cells  of,  335 
Semilunar  fold,  576 

ganglion  of  V,  474 
Senses,  common,  436 

general,  436 

special,  436 
Sensory  decussation,  485 

path,  general,  441,  461,  462,  474,  491, 

524 

peripheral  nerves,  426 
Septa  renis,  320;  see  Kidney 
Septo-marginal  tract,  467 
Septum  lingua;,  224 
Serial  sections,  15 
Serous  cells,  221 

membranes,  165 
Sertoli,  cells  of,  335,  378 

columns  of,  335 
Sewell  and  Langley  concerning   secretion, 

272 
Sex  cells,  378 

Sharpey,  showing  bone  lamella;,  191 
Sharpey's  fibres,  192,  234 
Sheath  of  Hcnie,  136,  426 

medullary,  132,  134 

Neumann's  dental  sheath,  232 

of  Schwann,  132 

[>cri fascicular,  208,  425 

myelin,   134 
Sherrington  concerning  receptors,  436 
Short  fibre  tracts,  445 
Signet-ring  cell,  88 
Silver  nitrate  method,  (Jolgi,  35 

of  staining  intercellular  substance,  28 
Skein,  closed,  54 
Skeletal  system,  188 

articulatioDfi,  204 

bone-marrow,  192 

bonc&,  188 


Skeletal  sj^stem,  cartilages,  204 
Skin  and  its  appendages,  380 
blood-vessels  of,  399 
color  of,  384 
corium,  380 
corpuscles  of  Grandry,  431 

of  ]\Ieissner,  394,  432 

of  Ruffini,  394,  434 

of  Wagner,  394 
cuticle,  382 
derma,  380 
development  of,  395 
eleidin  of,  383 
end-bulbs  in,  430 
epidermis  of,  382 
glands  of,  384 
glandula;  sudoripara;,  384 
Golgi-Mazzoni  corpuscles  of,  394,  434 
hair  follicles  of,  387 
junction  of,  with  mucous  membrane 

of  mouth,  220,  384 
kcratohyalin  granules,  383,  387 
Krause's  end-bulbs,  394 
lymphatics  of,  394 
mammary  gland,  395 
IMerkel's  corpuscles  of,  431 
mitosis  of  cells  of,  383 
nails,  385 

nerves  of,  394,  430 
of  scrotum,  381 
Pacinian  bodies  of,  434 
panniculus  adiposus  of,  383 
pai)ilUc  of,  381 
])areleidin,  384 
])ars  ])apillaris,  381 
pars  reticularis,  380 
peripheral  nerve  teiminations  in,  304, 

430 
prickle  cells  of,  383,  387 
retinacula;  cutis,  382 
.sebaceous  glands  of,  384,  391 
subcutaneous  tissue  of,  381 
sweat  glands  (glandula-  suboripara'), 

384 
pores  of,  384 
tactile  cells  of,  431 

corpuscles,  433 
Icchnic  of,  384 

for  l)loo(l- vessels  of,  305 
Vater-I'acinian  corpuscles  of,  394 
Small  intestines,  255 

agminated  follicles,  260 


634 


INDEX 


Small  intestines,  Auerbach's  plexus,  263 

blood-vessels  of,  268 

Brunner's  glands  of,  262,  273 

cells  of,  257 

chyle  capillaries  of,  270 

coats  of,  262 

crypts  of  Lieberkiihn,  260 

development  of,  296 

lacteals  of,  275 

lymphatics,  270 

Meissner's  plexus,  262 

migratory  leucocytes,  257 

muscle  of,  262 

nerves  of,  270 

Paneth's  cells,  260,  273 

Peyer's  patches  of,  260 

plexus  myentericus,  270 

replacing  cells,  259 

secreting  cells,  257,  272 

solitary  follicles,  260 

technic  of,  275 

valvulse  conniventes  of,  255 

villi  of,  256 
Smell,  organ  of,  584 
Smooth    muscle,    119;    see     Involimlary 

muscle 
Sodium  hydrate  as  a  macerating  fluid,  4 
Solitary  fasciculus,  487,  489 

follicles,  253 
Somatic  receptors,  473 

(peripheral)  neurones,  420,  473 
Somatochromes,  129 
Spaces  of  Fontana,  554 
Special  dental  germs,  238 

senses,  436 
Spermatids,  337,  344 
Spermatoblast,  345 
Spermatocytes,  337,  344 
Spermatogenesis,  58,  344 

technic  of,  346 
Spermatogones,  336 
Spermatozoa,  58,  337,  343 

acrosome,  337 

apical  body,  337 

axial  thread,  344 

development  of,  58,  344 

diagram  of,  343 

galea  capitis,  343 

perforatorium,  343 

structure  of,  58,  343 

technic  of,  346 
Sphenopalatine  ganglion,  436 


Spider  cells,  143 

Spinal  accessory  nerve,  483 

Spinal  cord,  416 

anterior  columns  of,  448 

funiculus,  448 

horns  of,  444,  448 

marginal     bundle    of    Lowenthal, 
466 

median  fissure,  448 

nerve  roots  of,  450,  459 

pyramids,  465 

white  commissure  of,  450 
antero-lateral  columns  of,  448 

fimiculus,  448 

white  column,  448 

ascending  tract,  463,  483,  487 

descending  tract,  466 
arachnoid  membrane  of,  422 
arrangement  of  fibres  of,  452 
arteries  of,  454 
ascending  tracts  of,  461 
blood-vessels  of,  454 
cell-groupings  of,  450 
cells  of  dorsal  horn,  450 
cells  of  the  intermediate  gray  matter, 

450 
of  Golgi,  Type  II,  446 
of  ventral  horn,  451 
cells   outside   cord,    with   axones   to 

white  matter  of  cord,  444 
central  canal  of,  416,  449 

gelatinous  substance,  449 
cervical  enlargement  of,  446,  455 

segments  of,  446 
Clarke's  column  of,  450,  455.  463 
coccygeal  segments  of,  446 
collaterals  of,  447 
column  of  Burdach,  459,  461 
column  of  GoU,  459,  462 
cells,  444,  461 

hecateromeric,  444 
heteromeric,  444 
tautomeric,  444 
comma  tract  of  Schultze,  467 
conduction  paths  of,  421,  461 
cornua  of,  448 

crossed  pyramidal  tract,  464 
descending  paths  from  higher  centres, 
464 
tract  from  Deiter's  nucleus,  466 
from  vestibular  nuclei,  466 
diagram  showing  tracts  of,  460 


INDEX 


635 


Spinal    cord,  direct    ascending   paths    to 
higher  centres,  461 

cerebellar  tract,  463 

pyranaidal  tract.  464 

reflex  collaterals,  452 
dorsal  graj'  columns,  448 

commissure,  449 

spino-cerebellar  tract,  463 

white  columns,  448 
dura  mater  of,  422 
ependyma  of,  453 
fasciculus,  medial  longitudinal,  467 

of  Thomas,  467 
fibre  tracts  of,  459 

methods  of  determining,  459 
filura  terminale  of,  442 
finer  tructure  of,  453 
fundamental  columns  of,  445,  468 
ganglion  cells  of,  443 
gelatinous  substance  of  Rolando,  449 
general  topography  of,  448 
Gowers'  tract,  463,  464,  465 
gray  matter  of,  420,  449 
ground  bundles  of,  445,  468 
Helweg's  tract,  464 
interchange  of  fibres,  452 
intermediate  gray  matter,  450 
intermedio-lateral  column,  450 
lateral  horn  of,  450 
long  ascending  arms  of  dorsal  root 

fibres,  461 
long  ascending  fibre  tracts,  445 
longitudinal    section    of    six    days' 

chick  embryo,  447 
lumbar  enlargement  of,  443,  448 

segments  of,  443 
main  motor  fibre  systems  of,  418,  441 
marginal  bundle  of  Lowenthal,  466 
marginal  zone,  449 
medial  fillet  (lemniscus),  462 
medullated  fibres  of,  406,  443 
membranes  of,  422 

arachnoid  422 

blood-vessels  of,  424 

dura  mater,  422 

pia  mater,  422 

spinal  dura,  422 

tcchnic  of,  424 
mixed  spinal  nerve,  424 
motor  cells  of  anterior  horn,  444 
multipolar  ganglion  cells  of,  112,  127 
439.  444 


Spinal  cord,  neiuroglia  cells,  453 

fibres,  453 

tissue,  450 
neurone  systems  of,  421 
nucleus,  Darkschewitsch's,  465 

Deiter's,  466 

funiculi  cuneati,  462 
gracilis,  462 
origin  of  fibres  of  white  matter,  443 

of  posterior  columns  of,  443 
oval  bundle  of  Flechsig,  463 
peripheral  motor  or  efferent  neurone 
system,  418,  441 

sensory  or  afferent  neurone  system, 
419,  426 
pia  mater,  spinaUs,  422,  448 
plexus  of  fine  fibres,  452 
posterior  columns,  443,  448 

funiculus,  448,  461 

horns,  445,  448 

median  septum,  448  ' 

nerve  roots,  450 

root  fibres,  450 
postcro-lateral  grooves,  448 

sulci,  448 
pyramidal  decussation,  464 

tracts,  464 
reflex  arcs,  469 
reticular  process,  448,  455 
root  cells,  441,  444,  451 
rubro-spinal  tract,  466 
sacral  segments  of,  446 
scheme  of  neurone  relations  of,  460 
section   through   cervical   enlarge- 
ment of,  405 

through  lumbar  enlargement,  448 

through        mid-thoracic       region, 

455 
through  six-day  chick  embryo,  447 
through  twelfth  thoracic  segment, 

455 
segments  of,  443 
septo-marginal  tract,  467 
shape  of,  443 

short  fibre  systems  of,  445,  462,  468 
shorter  intersegmental  ir.nK    ,](>H 
size  of,  443 

sj)ino  tcctal  tract,  465 
thalamic  tract,  462 
Iccto-spinal  tract,  465 
lechnic  of,  446,  471 
thoracic  segments  of,  443 


636 


INDEX 


Spinal  cord,  tract  from  interstitial  nucleus 
of  Cajal,  465 
tractus  cerebro-spinalis,  464 
cortico-spinalis,  464 
pallio-spinalis,  464 
reticulo-spinalis,  467 
spino-cerebeUaris  dorsalis,  463 
cerebellaris  ventralis,  463 
spinalis,  468 
thalamis,  414 
variations  in  structure  at  different 

levels,  455 
veins  of,  454 

ventral  gray  columns,  448 
commissure,  449 
spinal  cerebellar  tract,  463 
white  columns,  448 
vestibulo-spinal  tract,  466 
von  Monakow's  tract,  466 
white  commissure,  450 
matter,  420,  446,  450 
zona  spongiosa,  449 

terminalis,  450 
zone  of  Lissauer,  443 
Spinal  ganglia,  426 

amphicytes,  427 
capsule  of,  426 
development  of,  418 
technic  of,  446 
ganglion  cells,  436,  443 
central  processes  of,  436 
classification  of,  427 
collaterals  from,  47 
descending  arms  from  central  pro- 
cesses of,  436 
development  of,  418 
Dogiel's  classification,  427 
ectodermic  origin,  416 
modes  of  termination  of  peripheral 

processes  of,  429 
peripheral  processes  of,  429 
Rufifini's     classification    of    termi- 
nations    in     muscle      spindles, 

434 
satellite  cells,  427 
structiure  of,  426 
technic  of,  441,  446 
Spinal  nerves,  424 
Spindle,  achromatic,  54 
Spino-cerebellar  tract  (dorsal),  463 

(ventral),  426,  463 
Spino-collicular  tract,  462 


Spino-peripheral  motor  neurone  system, 

442 
Spino-spinal  tract,  468 
Spino-tectal      tract,      465,      483,      487, 

490 
Spino-thalamic  tract,  462,  483,  501,  504, 

515,526 
Spiral  ganglion,  475,  493 

lamina,  577 

ligament,  577 

limb  us,  582 

organ, 579 

prominence,  579 

sulcus,  external,  579 

terminations,  434 
Spireme,  closed,  54 

open,  55 
Spireme-thread,  54 
Splanchnic  effectors,  473 
Splanchnic  (peripheral)  neurones,  419 
Spleen,  181 

ampullae,  183 

blood-vessels,  182 

cavernous  veins,  183 

cells  of,  184 

central  arteries  of,  183 

connective  tissue  framework,  181 

cords  of,  184 

corpuscles  of,  182 
-development  of,  186 

function  of,  186 

development  of,  186 

germinal  centres  of,  182 

lymphatics  of,  186 

Malpighian  bodies,  182 

MolHer,     concerning     splenic    pulp, 

18s 

nerves  of,  187 
Spleen,  penicillus,  183 

pulp  of,  184 
cords  of,  184 

spindles  of,  183 

technic  of,  187 
Spleen-sinus,  183 
Splenic  corpuscles,  182 

pulp,  184 
Spheno-lymph  nodes,  174 
Spongioblasts,  142,  413 

of  His,  417 
Spongioplasm,  44 
Spongy  bone  (cancellous),  188 

primary,  202 


INDEX 


637 


Staining,  17 

differential,  3 

double   with    h;ematoxyHn-eosin,    20 
in  bulk,  21 
methods,  special,  28 
chloride  of  gold,  28 
Golgi's  chrome  silver  for  secretorx- 

tubules,  29 
Jenner's,  for  blood,  31 
Mallor>''s  aniline  blue  for  connec- 
tive tissue,  30 
phosphomolybdic     acid     ha?ma- 
toxylin    stain    for    connective 
tissue,  29 
phosphotungstic  acid  ha?matoxy- 
lin    stain    for   connective  tis- 
sue, 30 
Alaresh's  modification  of  Bielsch- 
owsky's  stain  for  fine  connective 
tissue  fibrils,  31 
osmic  acid,  for  fat,  31 
silver  nitrate,  for  intercellular  sub- 
stance, 28 
Verhoeff's  differential  stain  for  elas- 
tic tissue,  28 
Weigert's  elastic-tissue  stain,  28 
paraffin  sections,  23 
sections,  20 

double    with      hjematoxylin-eosin, 

20 
triple  with  haematoxylin-picro-acid- 

fuchsin,  21 
with  picro-acid-fuchsin,  20 
mth  picro-carmine,  21 
selective,  3 

special  neurological  methods,  32  * 
Cajal's  methods  for  neurofibrils  in 

nerve  cells,  37 
Cox-golgi  method,  36 
Golgi  bichlorid  method,  36 

silver  method,  35 
Marchi's,  for  degenerating  nerves, 

34 
Nissl's  method,  38 
Weigert's,    for    mcdullalcd    nerve 

fibres,  32 
Weigcrt-I'a!  method,  a 
Stains,  nuclear  dyes,  17 

plasma  dyes,  19 
Stalked  hydatid,  342 
Supcs,  574 
Stellate  cells,  510,  536 


Stenoni,  duct  of,  277 

Stohr,,  concerning  muscle  fibres   119 

scheme  of  spleen,  183 
Stomach,  247 

acid  cells  of,  245,  249 
adelomorphous  cells  of,  249 
Auerbach's  plexus,  270 
blood-vessels  of,  268 
cardiac  gland  of,  252 
chief  cells  of,  249 
delomorphous  cells  of,  249 
development  of,  296 
epithelium  of,  248 
fundus  glands  of,  249 
gastric  glands  of,  249 

pits  of,  248 
Heller's  plexus,  268 
lymphatics  of,  270 
]Meissner"s  plexus,  270 
mucous  membrane  of   248 
muscular  coat  of,  254 
nerves  of,  270 
oxyntic  cells,  249 
parietal  cells  of,  249 
peptic  cells  of,  249 

glands  of,  249 
plexus  myentcricus,  270 
pyloric  glands  of,  252 
replacing  cells,  252 
ruga;  of,  248 
secretion  of,  272 
solitary  follicles  of,  253 
stroma  of,  252 
technic  of,  254 
tubules  of,  250 
Stomata,  165 
Stratum  cinereum,  522 
corncum,  383 
cylindricum,  382 
fibrosum,  205 
germinativum   382 
granulosum,  355 
lemnisci,  522 
lucidum,  383 
Malpighii,  383 
mucosum,  382 
0|)licum,  522 
spinosum,  383 
submuscosum,  366 
su|)ravascularc  366 
vasculare  366 
zonule,  532 


638 


INDEX 


Stratum  cinercum,  synoviale,  205 
Streaming  of  protoplasm,  52 
Stria  cornea,  531 
medullaris,  530 
of  Baillarger,  541 
terminalis,  531 
vascularis,  579 
Striae  thalami,  522 
Styloglossal  j&bres,  224 
Subarachnoid  space,  422 
Subchorionic  placental  decidua,  374 
Subcutaneous  tissue,  318 
Subdural  space,  422 
Sublingual  gland,  277 

crescents  of  Gianuzzi  of,  278 
development  of,  of,  297 
duct  of  Bartholin  of,  278 
nerves  of,  280 
technic  of,  281 
Sublingualis  minor,  278 
Submaxillary  ganglion,  436 
gland,  278 

development  of,  297 
duct  of  Wharton  of,  278 
nerves  of,  280 
technic  of,  278 
Submucosa,  218 

Subperichondrial  ossification,  201 
Subperiosteal  ossification,  201 
Substantia  alba,  420 
grisea,  420 
nigra,  131,  517,  526 
propria  corneae,  550 
Sulcus,  external  spiral,  582 
Superficial  sensation,  436 
Superior  cerebellar  peduncles,  499,  500, 
502,  507,  517 
colliculus,  417,  517,  522 
gangUon  of  IX,  474 
longitudinal  fasciculus,  491,  500,  504 

S15   526 
olive  493,  500,  502,  504,  507 
Suprachorioidea  551 
Supraradiary  plexus  541 
Suprasegmental   arc  421 
brain  478 

cerebral  hemispheres  420,  478 
connections    (afferent    and    efferent) 
476 
corpora  quadrigemina,  420,  478 
intersegmental  nuclei  and  tracts  of 
segmental  brain,  479 


Suprasegmental  nuclei  and  tracts  form- 
ing suprasegmental  paths,  479 
pallium,  420,  478 
paths,  476 
afferent,  476 
efferent,  477 
peripheral    (segmental)    neurones, 

479 

structures,  478 

terminal  nuclei,  479 
.  neurones,  421 

afferent,  421 

associative,  421 

efferent,  421 
Suspensory  ligament,  565 
Sustentacular  cells,  284,  300,  335,  575 
Sweat  glands,  384 

development  of,  395 

ducts  of,  384 

muscle  tissue  of,  395 
pore,  384 
Sympathetic  ganglia,  418,  436 

cells  of,  439 

chain  ganglia,  436 

development  of,  418 

in  Auerbach's  plexus,  436 

in  Meissner's  plexus,  436 

pigmentation  of  cells  of,  439 

prevertebral  plexuses,  436 

structure  of,  436 

technic  of,  446 

termination  of  nerves,  440 

vertebral  ganglia,  436 
nervous  system,  416 
Synapsis  of  neurones,  138 
Synarthrosis,  204 
Synchondrosis,  204 
Syncytial  cells,  417 
Syncytium,  68,  373 
S5mdesmosis,  204 
Synovial  membrane,  205 

villi,  205 
System,  a,  68 

Szymonowizc,       showing      intercellular 
bridges,  74 
showing  meduUated  nerve  fibre,  136 

Tactile  cells,  431 

corpuscles,  223,  432 

of  Meissner,  432 

of  Wagner,  394  ] 
meniscus,  432 


INDEX 


639 


Taenia  thalami,  530 
Tapetum  celliilosum,  551 

fibrosum,  551 
Tarsal  glands,  568 
Tarsus,  56S 
Taste  buds,  226,  227,  432,  433,  587 

organ  of,  587;  see  Organ  oj  Taste 
Tautomeies,  445,  463 
Teasing,  4 
Technic,  general.  3 
Tecto-spinal  tract,  465,  483,  487,  490 
Teeth,  227 

apical  foramina,  228 
blood-vessels  of,  235 
cementum  of,  227,  233 
crown  of,  227 
cuticula  dentis.  233 
dental  germ,  238 

groove,  238 

papilla,  238 

periosteum,  234 

pulp,  228 

sac,  239 
dentinal  canals,  230 

fibres,  228 
dentine  of,  227,  228 
development  of,  238 

common  dental  germ,  238 

cuticular  membrane,  240 

dental  papilla,  238 

enamel  organ,  239 

special  dental  germ,  238 

technic  of,  242 

Tomes'  process,  ;<.40 
enamel  of,  227,  233 

cells,  237 

fibres,  233  » 

organ,  239 

prisms,  233 
fang  of,  227 

interglobular  spaces,  232 
layer  of  Weil,  228 
lines  of  Rctzius,  233 

of  Schreger,  232 
lymphatics  of,  236 
milk,  339,  241 
nerves  of,  236,  430 
Neumann's  dental  sheath,  232 
odontoblasts  of,  228 
peridental  membrane,  234 
permanent,  239,  242 
pulp  cavity,  227 


Teeth,  root  of,  227 

root-canal  of,  228 

special  dental  germs,  23S 

technic  of,  242 

Tomes'  granular  layer,  232 
process,  240 

true  molars,  242 
Tegmentum,  417,  47S,  483,  499,  515,  517 

central  tegmental  tract,  490,  499 

development  of,  417 

fillet,  462 

fourth  cranial  nerve,  515,  517 

lateral  lemniscus,  491,  493,  499,  501, 

504,  515 

nucleus  ruber,  436,  466,  476,  517,  524 

posterior  longitudinal  fasciculus,  491, 
500,  504,  515,  526 

reticular  formation,  476,  485,  487,  489, 
490,  491,  501,  504,  507 

superior  colliculi,  417,  517,  522 
peduncles,  499,  500,  502,  507,  517 
Telencephalon,  417,  532 
Telophragma,  117 
Telophase,  56 
Tendon,  structure  of,  91 

sheaths,  208 
Tendon-muscle  junction,  208 

organs  of  (Jolgi  in,  434 

peripheral-nerve  terminations  in,  434 
Tenon,  capsule  of,  566 
Tensor  chorioide^,  554 
Terminal  arborizations,  131,  429 

bronchus,  310 

nucleus,  421,  490 
Terminations,  nerve,  429 

armular,  434 

arborescent,  434 

RufTini's  theory  of,  434 

spiral,  434 
Testis,  233 

blood-vessels  of,  342 

corjius  Ilighmori,  23;^ 

dcveloi)ment  of,  376 

ducts  of,  334,  339,  342 
cjaculatory,  341 

epididymis  of,  333 

lobules  of,  333 

lym|)lialics  of,  342 

mediastinum,  333 

nerves,  342 

rctc,  339 

secretion  of,  343 


640 


INDEX 


Testis,  semen,  343 

seminal  ducts  of,  339 
vesicles,  341 

seminiferous  tubules  of,  334 

spermatozoa,  337,  343 

technic  of,  346 

tunica  albiiginea  of,  333 
vaginalis,  333 
vasculosa,  333 

vas  deferens,  334 
Thalamencephalon,  522 
Thalamo-cortical  neurones,  462,  523 
Thalamus,  417,  523,  526,  530 

anterior  peduncle  of,  536 

bundle  of  Vicq  d'Azyr,  524 

external  segment  of  5  23 

geniculate  bodies,  520 

internal  segment  of,  523 

mamillo-tlialamic  tract,  524 

metathalamus,  523 

nuclei  of,  523 

nucleus  of  Luys,  5  23 

pulvinar,  523,  524 

Sachs,    E.,    concerning    the,    523, 

524 

thalamic  radiations,  523,  526 
Theca  folliculi,  356 

Theoharra  and  Bensley  concerning  secre- 
tion, 272 
Thermostat,  13 
Thermotaxis,  51 
Thionin,  19 

Thomas,  fasciculus  of,  467 
Thoracic  duct,  165 

technic  for,  166 
Three-neurone  afferent  suprasegmental 
conduction  path,  421 

spinal  reflex  arc,  469,  506 
Thrombocytes,  108 
Thymus,  175 

blood-vessels  of,  177 

development  of,  177 

Hassall's  corpuscles,  176 

lymphatics  of,  177 

nerves  of,  177 

technic,  178 
Thyreoid,  402 

absence  of,  403 

blood-vessels  of,  403 

cartilage,  301 

cells  of,  403 

colloid  of,  402 


Thyreoid,  development  of,  403 

isthmus  of,  402 

lymphatics  of,  403 

nerves  of,  403 
Timofeew,    concerning    nerve    fibres    in 

prostate  gland,  348 
Tissue,  68 

-elements,  dissociation  of,  4 
Tissues,  67 

adipose,  87 

areolar,  87 

blood,  103 

bone,  100 

cartilage,  97  , 

classification  of,  69 

connective  80,  82 

derivatives  from  ectoderm  entoderm, 
mesoderm,  67,  68  ' 

dissociation  of,  4 

elastic,  92 

embryonal,  82 

endothelium,  77 

epithelial,  70 

erectile,  349,  376 

examination  of  fresh,  4 

histogenesis  of,  67 

lymphatic,  164 

lymphoid,  170 

mesothelium,  77 

muscle.  III 

nerve,  126 

osseous,  100 

osteogenetic,  197 

reticular,  94,  170 

subcutaneous,  381 

subserous,  268 

white  fibroi)^,  82 
Toluidin  blue,  19 
Toluol,  as  solvent,  13 
Tomes' granular  layer,  231 

process,  240 
Tongue,  223 

blood-vessels  of,  226 

circumvallate  papillae,  225 

connective  tissue  of,  224 

Ebner's  glands,  226 

end-bulbs  of  Krause,  227 

fibres  of,  224 

filiform  papillae,  225 

fungiform  papillae,  225 

glands  of,  222,  226 

longitudinal  fibres  of,  224 


INDEX 


641 


Tongue,  lymph  follicles  of,  226 
spaces  of,  227 

muscles  of,  2  23 

nerves  of,  227 

papilla?  of,  225 

septum  lingua,  224 

taste  buds,  226,  227,  432,  5S7 

tcchnic  of,  227 

transverse  fibres  of,  224 

vertical  fibres  of,  224 
Tonsils,  1/8 

blood-vessels  of,  180 

cr)-pts  of,  179 

development  of,  180 

germ  centre  of,  179 

lingual;  fcUiculae  linguales,  180 
foramen  caecum  lingui  of,  180 

lymphatics  of,  180 

lymphoid   infiltration  of   epithelium, 
179 

nerves  of,  180 

nodule  of,  179 

palatine  or  true,  178 

pharyngeal,  180 
adenoids  of,  180 

salivary  corpuscles  of,  180 

technic  of,  181 
Trachea,  301 

blood-vessels  of,  303 

cartilages  of,  302 

glands  of,  302 

lymphatics  of,  304 

ner\'es  of,  304 

technic  of,  304 
Tract,  a,  421 

antero  -  lateral    ascending  -ventral 
spino-cerebellar,  463 

antero-latcral  descending,  466 

Burdach's,  459,  462 

central  tegmental,  490,  501,  507 

cerebro-sfiinalis,  464 

cochlear,  491,  500,  504 

comma,  of  Schultze,  467 

corlico-spinalis,  464 

crossed  [)yramidal,  464,  485 

Dcilcro-spinal   tract,  4()(>,  483,  487, 
490,  502 

descending  from   pallium   to   motor 
nuclei,  533 

from  interstitial  nucleus  of  Cajal,46s 

485,  487 
41 


Tract    from   nucleus  of   posterior   longi- 
tudinal fasciculus,  465 
from  vestibular  nuclei,  466 
direct  cerebellar,  463 

pyramidal,  465 
dorsal  spino-cerebellar,  463,  483,  487, 

490.  507 

dorso-lateral  ascending — dorsal  spino- 
cerebellar, 463 

fasciculus  of  Thomas,  467 

fastigio-bulbar,  500,  502 

fundamental  or  ground  bundles,  445, 
468 

Flechsig's,  463 

Goll's,  459,  462 

Gower's,  464 

Helweg's,  467 

intersegmental  (shorter)  46S 

Lissauer's,  443,  450 

long  ascending  arms  of  dorsal  root 
fibres,  461 

mamillo-lhalamic,  524,  532 

marginal  bundle  of  Lowcnthal, 
466 

medial  lemniscus,  462,  485,  487,  489 

491,  493,  517 
optic,  524 

oval  bundle  of  Flechsig,  463,  467 
pallio-spinalis,  464,  533 

-tectal,  535 
posterior,  462 

funiculi,  461 
predorsal,  491 

•fasciculus,  517 
Iiyramidal,  464,  533 

anterior,  465 
rubro-spinal,  466,  483,  487,  490,  504, 

SIS 
secondary  cochlear,  493,  504,  507 
vagoglossopharyngeal  and  trigem- 
inal, 515,  526 
vestibular,  493 
scpto-marginal,  467 
short  fibre,  445,  4^>2.  4^8 
spinalis  trigemini,  485,  500 
spino-(erei)cilar,  ventral,     463,    483, 
487,  501 
-colliculo,  465,  4?,^,  4S7,  490,  502, 

504,  507,  S«7 
-spinal,  468 
-tectal,  465,  483,  487,  490 


642 


INDEX 


Tract,  spinothalamic,  462,  483,  501,  504, 
515,526 
tecto-spinal,  465,  483,  487,  490 
uncrossed  cerebellar,  463 
ventral    spino-cerebellar,    463,    501, 

504,  51 5 

vestibulo-spinal,  466 

Von  Monakow's,  466 
Tractus,  see  Tract 
Transitional  leucocytes,  105 
Transverse  temporal  gyri  of  Heschl,  541 
Trapezoid  nucleus,  493 
Trapezium,  493 
Trigeminus  (V  nerve),  475,  485,  489,  493, 

501,  504,  506 
Trigonum  hypoglossi,  481,  489 

olfactorium,  532 

vagi,  481 
Trochlearis  (IV  nerve),  475,  515,  518,  520 
Trophic  centre  of  neurone,  137 
Trophospongium,  46 
True  corpora  lutea,  360 

tonsils,  178 

vocal  cords,  301 
Tuberculum  cinereum,  481,  531 

olfactorium,  532  , 

Tubular  glands,  215 
Tubules  arched,  320,  323 

collecting  321,  324 

distal,  320,  323 

first  or  proximal,  320,  322 

intercalated,  276 

intermediate,  277 

junctional,  377 

salivary,  276 

second  or  distal,  320,  323 

secreting,  276 

seminiferous,  334 

serous,  222 

straight,  321,  324 

uriniferous,  320 
Tubulo-alveolar  gland,  282 
Tunica  albuginea,  of  ovary,  353 
of  penis,  349 
of  testis,  2)iZ 

dartos,  381 

fibrosa,  356 

vaginalis,  333 

vasculosa,  333,  356 
Two-neurone  spinal  reflex  arc,  469,   504 
Tympanic  gland,  412 

membrane,  573 


Tympanum,  573;  see  also  Ear,  middle 
Tyson,  glands  of,  351 


Ultimate  fibrillas,  115 
Uncinate  fasciculus,  535 
Unipolar  nerve  cells,  127,  428 
Ureter,  329 

development  of,  376 
technic  of,  331 
Urethra,  female,  351 

glands  of  Littre  of,  351 
male,  351 

fossa  navicularis,  352 
glands  of  Littre  of,  352 
technic  of,  352 
Urinary  bladder,  330 
blood-vessels  of,  331 
development  of,  376 
system,  318 

development  of,  376 
technic  of,  331 
kidney,  318 

-pelvis,  329 
ureter,  329 
urinary  bladder,  330 
technic  of,  331 
Uriniferous  tubule,  320 

arched  tubule  of,  321,  323 
ascending  arm  of  Henle's  loop,  320, 

323 
blood-vessels  of,  325 
Bowman's  capsule,  320,  322 
descending    arm    of    Henle's    loop, 

320,  322 
development  of,  376 
duct  of  Bellini,  321,  324 
epithelium  of,  3  24 

first  or  proximal  convoluted,  320,  322 
foramina  papillaria,  321 
glomerulus,  320 
Henle's  loop,  320,  323 
location  in  kidney  of,  3  24 
Malpighian  body,  321 
membrana  propria  of,  321 
neck  of,  322 
renal  corpuscle,  320 
Ruble,  concerning,  325 
second  or  distal  convoluted,  3  20,  3  23 
straight  or  collecting,  321,  324 
Uterus,  366 

blood-vessels  of,  375 


INDEX 


6-43 


Uterus,  cen-ix,  367 
coats  of,  366 
decidua  basalis,  370 

capsularis,  370 

graviditatus,  370 

menstrualis,  369 

reflexa,  370 

serotina,  370 

subchorionic  placental,  374 

vera,  370 
decidual  cells  of,  370 
development   of,   376;    see   also   Re- 
productive system,  development  of 
lymphatics  of,  375 
masculinus,  248 
mucosa  of  menstruating,  368 

of  pregnant,  370 

of  resting,  367 
stratum  submucosum,  366 

supravasculare,  366 

vasculare,  366 
nerves  of,  375 
placenta,  371 
plicae  palmatae,  368 
pregnant,  370 

theories  concerning,  369 
stage  of  menstruation  proper,  369 

of  preparation,  368 

of  reparation,  369 
technic  of,  379 

with  placenta  in  situ,  technic  of,  379 
Utricle,  575;  see  Sacctde  and  utricle 
Utericulo-saccular  duct,  575 
Utriculus  prostaticus,  348 
Uvula,  mucous  membrane  of,  220 


Vagina,  375 

blood-vessels  of,  376 

coats  of,  375 

lymphatics  of,  376 

nerves  of,  376 

rugjc  of,  376 

technic  of,  376 
Vagus  (X)  nerve,  474,  489 
Valve,  Ilcisterian,  295 
Valves  of  heart,  162 

of  veins,  158 
Valvula;  conniventes,  246,  255 
Vas  deferens,  340 

technic  of,  346 

qiididymis,  340 


Vasa  effercntia,  339 

vasorum,  159 
Vascular  papillae,  381 

system,    151;    see    also    Circulatory 
system 
Vater-Pacinian  corpuscles,  394 
Veins,  158 

adventitia  of,  158 
arcuate,  328 
central,  289 
coats  of,  15S 
development  of,  163 
intima  of  158 
lymph  channels  of,  159 
media  of,  158 
musculature  of,  158 
nerves  of,  158 

perivascular  lymph  spaces  of,  159 
portal,  289 
renal,  318 
splenic,  182 

stellate,  of  Verheyn,  328 
sublobular,  289 
technic  of,  160 
valves  of,  158 
vasa  vasorum,  159 
vena;  vorticosae,  551 
Venae  vorticosae,  551 
Ventral  spino-cerebellar  tract,  463 
Ventricles  of  brain,  416,  417,481,487,499 

of  heart,  161 
Verheyn,  stellate  veins  of,  328 
Verhorff's  differential  elastic-tissue  stain, 

28 
Vermiform  appendix,  265 

lymph  nodules  of,  266 
mcsoappendix,  265 
technic  of,  275 
Vermis  of  cerebellum,  415,  449,  4SS 
Vertebral  ganglia,  436 
Vesicle,  air,  310 
brain.  416 
germinal,  59 
optic,  569 
otic,  583 
seminal,  342 
Vesicula  prostatica,  348 
Vestibular  ganglion,  425 
nerve,  425,  44' 
nuclei,  441 

descending  tract  from,  441 
Vestibule,  575 


644 


INDEX 


Vestibule,  ductus  reuniens  of,  575 

endolymphatic  duct,  575 
sac,  575 

saccule  of,  575 

utricle  of,  575 

utriculo-saccular  duct  of   575 
Vestibulo-semicircular  canal  group  of  seg- 
mental neurones,  475 
Vicq  d'Azyr  bundle  of,  524,  532 
Villi,  256 

development  of,  297 

fastening,  371 

floating,  371 

free,  371 

lacteals  of,  275 

synovial,  205 

terminal,  371 
Visceral  neurones,  419,  475 

peritoneum,  267 
Visual  areay  488 

group  of  segmental  neurones,  475 

path,  475,  524 

purple,  557 
Vision,  organ  of,  548 ;  see  Organ  of  Vision 
Vital  properties  of  cells,  50,  213 

function,  51 

irritability,  51 

metabolism,  50,  213 

motion,  51 

reproduction,  52 
Vitreous  body  of  the  eye,  565 
Cloquet's  canal,  565 
hyaloid  canal  of,  565 

membrane  of  chorioid,  553 
of  iris,  553 
Vocal  cords,  301 
Volkmann's  canal,  191,  196 
Voluntary  striated  muscle,  114;  see  Mus- 
cle, striated,  voluntary 
Von  Bechterew's  nucleus,  500,  507 
Von  Bibra,  concerning  chemical  composi- 
tion of  dentine,  228 
of  enamel,  233 
Von  Gudden,  concerning  method  of  deter- 
mining fibre  tracts  of  cord,  459 
Von  Monakow's  bundle,  466 

Wagner,  corpuscles  of,  394 
Wallerian  degeneration,  law  of,  141 


Wandering  cells,  83 
Washing  after  fixation,  9 
Weigert's  elastic-tissue  stain,  28 

hcematoxylin,  19 

method  of  staining  meduUated  nerve 
fibres,  32 
Weigert-Pal  method,  33 
Weil,  layer  of,  228 
Wernicke,     perpendicular     fasciculus    of, 

535 
Wharton's  duct,  278 
Wheeler,  showing  amitosis,  52 
White  blood  cells  (leucocytes),  105 

or  fibiillated  fibres,  86 

fibrous  tissue,  82 

matter,  420,  450 

rami  communicantes,  425,  436 
Wilson,  E.  B.,  diagrams  showing  mitosis, 

54,  56 
Wirsung,  duct  of,  281 
Wolffian  body,  338,  377 
Wrisburg,  cartilage  of,  301 

nerve  of,  501 

Xylol  and  cajeput  oil  for  clearing,  23 

-balsam,  23 

damar,  30 
Xylol-paraffin  for  embedding,  13 

Yellow  or  elastic  fibres,  86 
Yolk  granules,  357 

Zenker's  fluid  for  decalcifying,  10 

for  fixation,  8 
Zinn,  zonule  of,  565 
Zona  incerta,  530 

pectinata,  580 

pellucida,  61,  357 

spongiosa,  449,  450 

tecta,  580 
Zone  of  Lissauer,  443 

of  oval  nuclei,  300 

of  lound  nuclei,  300 
Zonula  ciliaris,  565 
Zonule  of  Zinn,  565 
Zuckerkandl,  organ  of,  412 
Zymogen  granules,  282 

technic  of,  287 


C£8l638)MSO 


